
Stupidity: When the crew of the German U-boat boards Katanga's ship, the submarine moves in a position perpendicular to the ship's bow as if to block its path. In reality, this would have been a pretty stupid move by the German captain, as Katanga could have rammed the submarine easily. Any kind of damage to the hull, especially ramming damage (even from small ships), would have been catastrophic to the submarine. It makes no sense to make a manoeuvre like this.

Stupidity: Shriek is being taken to a new facility for superbeings, after a medical exam established that her sonic powers that she has been using since she was a kid are too strong to keep her at the correction house. So "naturally" for this transport she is not gagged, sedated, not even bound, and there's just one guy with her, not even wearing earplugs. It couldn't possibly be any more comically unsafe.

Stupidity: Why, in the most secure computer room you could find, with all those detection devices, did they not install video cameras? There is no risk of a security breach as they could be locked into a position that would not show the computer screen or keyboard but would show that an intruder had entered the room.

Stupidity: Bori Khan is a skilled archer and a man without honor. He's not fighting fair, and cares just to win, as established and explicitly said. He shoots an arrow at Mulan, the Witch gets in the arrow's way sacrificing herself to protect her...and for no reason whatsoever he does not shoot anymore, giving the chance for the two girls to share their very special dramatic moment together, but creating a colossal plot contrivance. It is a know movie cliche for the fight to 'pause' around the main character, but here we have a sniper who desists completely (he won't shoot anymore) for absolutely no reason. (01:29:00)

Stupidity: At the beginning, young Indy knocks out the driver of the car, pulls him out, and just leaves him on the ground by the car while entering the car. Neither the knockout nor the unconscious driver lying around are noticed by any Germans in the vicinity. Not even by the soldier who opens the car door and the officer who gets into the car, both of whom immediately appear after Indy has gotten into the car. (00:06:00)

Stupidity: If Jordan was inside the cake and the cake was right there in the room when the takeover began how did the bad guys forget she was still inside?

Stupidity: When the Keymaker is closing the door to the room that leads to the Source, he stands in the doorway resulting in the multiple Agent Smiths gunning him down. He could have easily closed the door without standing in the doorway and consequently would have lived.
Suggested correction: Who says the door was bullet proof and the Keymaker couldn't have been shot through the door?
The point of the stupidity is that he shouldn't have been in the doorway at all, even if the door wasn't bulletproof, there was no need for him to even stand behind the closed door. He could have pushed the door closed from the side.
It seems to be a heavy door, he simply couldn't close it with just his arm, thus he had to move his body forwards in order to close it. In that brief moment he got shot before the door closed. He could have for example kicked the door shut but he simply didn't think of that at that moment, also not knowing the Smiths were about to fire a volley of bullets at them.

Stupidity: Monk steals the magazine from Coffey's SIG. However, I don't see how he could have jacked the slide to eject the round in the chamber without being noticed. Someone as paranoid as Coffey was at this point would not have left the chamber empty. (Just FYI, when you load an automatic pistol with a magazine, you have to pull back and release the slide to load the first bullet in the barrel.)
Suggested correction: Since we are never shown that Coffey did chamber a round, we cannot assume that he did based on his personality alone. Therefore this isn't a plot hole. However, it is ridiculous that he is threatening people with a gun without a chambered round. This entry should be listed as "Stupidity."
SEALs don't carry weapons without a round chambered. The "maybe" here falls much more on the side of the round being in the chamber. And "Stupidity" wasn't an option available when this entry was originally submitted. :).

Stupidity: Reliant's prefix code is 16309. This code prevents an enemy ship from ordering a friendly ship to lower its shields or something similar. Five digits with no symbols. We know that symbols and letters aren't used since Spock uses a 10 digit set of switches to input the code. This is ludicrous. In 2016, a high powered server could crack a 6 digit password in approximately 0.0224 seconds (at 100 billion guesses/second). Any starship computer would have to far more processing power then a 2016 server. The prefix code protecting a starship from cyber attack would have to be insanely complex in order to be useful.
Suggested correction: Keep in mind the era that this movie was made in. This movie was made before PCs really existed. Computers at this time were typically huge devices or box like containers. Their data storage capacity was minuscule and there certainly wasn't any form of AI logic programs built to "hack" passwords. I know this movie is about space and set in the future but there's a lot of stuff in Star Trek movies that based on our technology or development currently, we would expect something bigger, smarter, etc. We still have problems today with people using archaic password structures like 1.2.3.4. or actually using the word password for/in their password. Back in '81-'82, I'm sure that most people would not have thought about codes being hacked. This is not to mention that in many movies, which I don't know if there is a specific reason for using 16309, codes, passwords, numbers for addresses/apt#/room#/etc and other info frequently come about as tribute, honoring, or coming from something in the lives of a film's director/producer/actor/etc! So sure with today's technology, which could have been accomplished more than 10 years ago as well, using a single string of numbers as security measures for anything is foolish and can be hack by a self running password-like cracker program... But they made this "code" back in the very early 80s when computer hacking was barely unconscionable (MAYBE) so unless these #s were a tribute or to honor something, I'm pretty sure no one was even thinking of hacking back then... We all aware of today... all about the hacking threats and YET we still have people using 1.2.3.4., the word password, or other horrible predictable password choices that can easily be broken by a password cracking program... And we know that there's a huge hacking threat requiring strong security measures but don't do so while back then, there was little awareness of the threats of hacking much less the concept of hacking altogether.
OR... in this future they have limited the number of password attempts to one a day and the ship automatically goes to red alert after a failed attempt until the right code is entered. That way it would take 7,327 years or so to try all the codes with the crew on notice and plenty of time to address the threat.

Stupidity: Oddjob brings the crushed cube of the Lincoln back to the stud farm so that Goldfinger can "separate my gold from the late Mr Solo." Oddjob could have simply removed the gold from the trunk of the Lincoln before having it crushed.

Stupidity: When the invasion of planet P begins, we see the Rodger Young get hit. In the explosion sequence, we are treated to people sitting around tables in what can only be described as a mess hall exploding. In a military environment, this would be a time where everyone would be at their "battle stations". Nobody would be having chow or off-time when the ship is expecting combat. In this case, it was a planned troop landing.
Suggested correction: Yes, it was stupidity, but it was an intentional depiction that supports the plot. During the landing, the Captain is completely surprised by the bombardment and says something like, "This isn't light uncoordinated resistance." The fleet's lack of preparedness at Planet P is a major plot point that later results in the replacement of the Air Marshal in command.
No, you are talking about a different sequence. When they are unprepared, they are doing an invasion of Klendathu, the Bug's home planet. This is earlier in the movie and the Rodger Young was only slightly damaged in that. The stupidity is about the invasion of Planet P at the end of the movie, where the Rodger Young is cut in half.

Stupidity: Early in the film, Peter Parker desperately wants to see Mary Jane's performance, but he is turned away at the theatre doors because he is a few minutes late. Defeated, Peter shuffles away and sulks. Seriously? Why couldn't Peter simply enter the theatre through a side door or the roof? He's Spider Man.
Suggested correction: There's two things to consider here. First, a major theme of the film is Peter struggling with keeping his Spider-Man and Peter Parker lives separate. Peter makes every attempt to get to the show on his own, as Peter by riding on his scooter. Simply breaking into the theater after he has been turned away would ruin the idea that keeping his two lives separate is a struggle. It would instead imply the opposite, that Peter can simply use his powers to solve his problems whenever it's convenient. Secondly, the usher makes it clear that no-one is to be admitted after the show has started as this would disturb the guests and possibly the performers as well. Sneaking into the theater could very well ruin the performance and Peter obviously wouldn't want that.
If there's one thing we know about Spider-Man, it's that he is incredibly stealthy, often coming and going without any detection whatsoever. He could have easily accessed the building and watched the show from a secluded vantage and even met Mary Jane backstage afterwards. Certainly in this case, using his powers would be justified, given that it was more important for Mary Jane to know Peter attended the show, rather than simply giving up.
He doesn't want to do any of that, though. He wants to go to the show as Peter, with a ticket, sit in a seat with the rest of the people, enjoy the show, and see Mary Jane afterwards. He stops the car chase as Spider-Man after his scooter is wrecked and instead of web-swinging to the theater, which would have been much faster, he chooses to change back into his regular clothes and drive the criminal's car. Sure, he certainly could have used his powers to get into the theater but the point is he doesn't want to. The fact that he chooses not to use his powers and instead deal with the consequences of hurting Mary Jane's feelings is the entire point.
And besides he'd probably get kicked out of the theater if he was caught.

Stupidity: A major effort is put in the future to develop the time portal, so they can recruit people from the past to help fight the war in the future. Yet they never seem to think to share anything with the past about the creatures and how to kill them or find out where they came from so the can help either prevent it from happening or help save the future before humanity is wiped out. Muri does recruit Dan for this purpose but it seems wasted to only use 1 person for this much more important goal.

Stupidity: Batman finds the Ice Princess on the edge of the roof, standing on the wall. If she's no longer bound, why didn't she just jump down onto the roof and negate the risk of falling to her death, which she did?

Stupidity: Hans keeps a major part of his plan secret from his own team: that the electromagnetic lock will be disabled if the FBI shuts down power to the building. The mercenaries hired as muscle don't need to know the minutiae of the plan, but it seems ludicrous that Theo wasn't told. Theo states on more than one occasion that he can't proceed past a certain point and that he hopes Hans has a plan for the final lock. Evidently, Hans was keeping this information secret simply to amuse himself, which makes little sense considering how much planning went into the heist.
Suggested correction: Or because he simply doesn't trust anyone with that kind of knowledge. He neither trusts them or cares about them, it's all him.
So he trusts that Theo would be on board with all the murder and mayhem, open all the other locks, be in a tactical lookout position when the police try to breach, and drive the getaway vehicle. But he doesn't trust Theo enough to tell him the last lock will open when the power goes out?
It's not about trust; Hans needs Theo to do what he is there for and that is all you mention up to the final lock. He has a plan for the final lock and so there's no need to discuss it with the team, since it won't be any of them responsible.
The more people that know the plan the more chances of someone talking. Especially when they are hired mercenaries.
Theo was already on board with taking hostages and committing murder. Him knowing that the power needed to be shut off to open the last lock doesn't appear to be particularly important information you would need to keep from someone to keep them from talking.
If he's the only one that knows the final step to get the money, then at least up until that moment he is absolutely indispensable to the plan and ensures no-one would double-cross him. In any case I'm not sure being more cautious than necessary really qualifies as "stupidity."

Stupidity: In the scene with the water-jug puzzle, both Zeus Carver and John McClane initially suspect that the small carrying case contains a bomb. McClane goes ahead and opens the case, which confirms that it is a bomb (the electronic readout in the case even says: "I AM A BOMB. YOU HAVE JUST ARMED ME"). If they suspected it was a bomb in the first place, why didn't Carver and McClane immediately try to warn the dozens of pedestrians all around them to evacuate the area before McClane opened it? That would be a seasoned police officer's first instinct. Instead, McClane and Carver banter and bicker and never attempt to warn the public, even as the timer is ticking down.
Suggested correction: This carries over from the very first time McClane and Zeus talk to Simon on the phone (the "As I was going to St. Ives" scene). Simon tells the two not to run and McClane assures him they won't but that there are at least 100 people on the street, to which Simon responds "That's the point." McClane takes this to mean he can't just warn everyone or Simon will set the bomb off. They open the case because they don't know that doing so will arm the bomb. They wanted to know if there was a riddle or more instructions. Having the bomb be armed by being opened, complete with the pithy text "you have just armed me" was just a way for Simon to torment McClane. The bantering and bickering is of course, still pretty stupid but is consistent with how the characters behave for the entire movie.
Still, McClane's whole motivation in this movie is to save innocent people from death, which goes above and beyond his motivation in the first movie (which was to save his wife). What is the whole point of disarming the briefcase-bomb in the park if not to save the public? As stated in the original post, no seasoned and dedicated officer of the law would proceed without warning the public.
Except he was told specifically earlier not to do that. If he warned people of the bomb, it was implied that Simon would remotely detonate it. It can't be "stupid" of McClane to not warn people if he thinks doing so will get them killed. I agree that it is a trite movie cliche that a cop doesn't act like a cop would in the real world, but in the context of this film McClane's actions are consistent with the instructions Simon gives him.

Stupidity: The eco-terrorists leave the Orca completely unattended allowing Madison to take it without anyone realizing until she is long gone. In addition, they don't post any guards at the exit of the bunker and Madison simply walks away without anyone noticing her at all.
Suggested correction: They leave the Orca in their empty command room within a bunker filled with loyal men. There is no way anyone could have broken in and stolen it. Madison had the advantage of already being in the bunker and even then had to navigate through the air ducts in order to steal the Orca and escape. They wouldn't have armed men visible immediately outside because they didn't want anyone to notice that they were there.
Either one of these issues by themselves wouldn't be particularly stupid but the combination of them both would indeed allow someone to just walk in and take the Orca. You don't need to post a visible guard at the exit, but nobody is watching the exit at all.

Stupidity: It was pure stupidity for Riggs to bring Rika back at her residence after escaping the hit on Riggs. The villains know where Riggs' love interest lives and this nor the option to hide somewhere else or safer never occurs to him?

Stupidity: There is no way a fighter with a brain would risk serious injury to themselves before a fight by continually punching a frozen rack of meat in a freezer slaughterhouse. There is nothing to gain by doing this, and it would only result in both fists being broken.
Suggested correction: In fact, Sylvester Stallone permanently damaged his knuckles filming the two scenes. He obviously did not realise how dangerous punching a side of beef would be, and it isn't out of the question that the character Rocky Balboa wouldn't realise this either.
It shouldn't take a rocket scientist to know that if you punch or hit anything with a bare fist against anything solid, rock hard, you will damage yourself badly.
Absolutely, it shouldn't, but that is not what the "Stupidity" category is for. It is unintelligent for someone to do this, but that is not a movie mistake. Sylvester Stallone really did punch that beef and really did injure himself, so it is not something that is out of the question for a character in a movie to do.
No, but it is out of the question for a man with painfully damaged knuckles to go fifteen rounds with a world heavyweight champion boxer. In fact, Rocky would probably have failed the compulsory pre-fight physical and would have been ruled unfit to fight.
Where in the movie is Rocky experiencing "painfully damaged knuckles"? With your logic, the fight would have most likely been called long before the 15th round, due to the very unrealistic and improbable punishment the 2 boxers were inflicting on each other.

Stupidity: When Han tells Drydon Vos that he and Tobias will steal unrefined coaxium from the mines on Kessel, Vos initially says no, as Crimson Dawn's relationship with the Empire would be at risk. Han then explains that the Empire wouldn't know they were working for Crimson Dawn. Vos then agrees but insists his top lieutenant Qi'ra accompany them, even though she is a known associate of Crimson Dawn and literally has their symbol branded on her wrist.