
Stupidity: The minivan is involved in multiple serious accidents but shows very little damage.

Stupidity: Why didn't they take out the crushed hand guy while the creature was fumbling inside the glove? Plenty of time to do it. Why did no one use a knife to stab the creature?

Stupidity: Liv and her five friends went to Willy's to set it on fire, but Liv insisted they first go inside to get the Janitor out. All were aware of the situation and danger related to the mass murderer and the animatronics, but Bobby and Kathy went into another room to "hook up." Kathy recognized the room as the one where the killers committed suicide and later saw movement, but she continued having sex with Bobby until he was attacked and killed. (00:38:48 - 00:42:02)

Stupidity: One of the actors microwaves bullets and then loads one into a weapon. Only problem: she/he (I did not pay attention) puts the round the wrong way around into the magazine. Then the person loads the magazine with the one round visible in the wrong direction into the weapon. I would say that this should not be working. (04:25:00)

Stupidity: They could've used the flying chopper thingy to kill off the armed guys when rescuing the kids off the train carriages. That way they could have made sure they got every single kid rather than rushing to just take the one containing Minho (which they messed up).

Stupidity: Why would 006 put Bond in a self destructing helicopter instead of just shooting him? Being Bond's old partner, he of all people should know how good of an escape artist Bond is.

Stupidity: It is pretty silly for Martin Lawrence to go undercover as a police officer when it would make way more sense to go undercover as a janitor/custodian since his main goal is to gain access to the vent. A janitor would be a way less conspicuous disguise than a detective and slipping through a backdoor entrance disguised as a janitor should not be all that complicated for someone as savvy as Myles. But of course this would make a far less entertaining film.

Stupidity: The fact that Nolte even gives in to Eddie's demands is ridiculous. Why not just interview him in prison, ask him where to look for certain people, etc, and if it's a dead end, report back and ask for further tips, etc. They had zero problem going to prison and asking Kirkland Smith in the sequel.
Suggested correction: He refused to tell him anything unless Kates takes him out of prison.

Stupidity: When the crew go to New York they are in the back of a fish truck carrying fish. There's no need for them to do that. So long as the truck looks normal outside to keep their cover, they could have the inside kitted out any way they want. When they get to the fish factory they open up the warehouse in front of the workers to reveal the cars, so the workers are in on it being a front - it makes no sense to actually have fish in the back of the truck.

Stupidity: All the mutants on the island need Magneto at the last second to take control of the missiles so they don't land and explode. Why didn't Azazel just teleport everyone off the island?
Suggested correction: Given the situation, there was probably very little time to come up with a plan like this. The missiles were flying towards them extremely quickly, and there would have been nowhere near enough time to band every single person together for Azazel to teleport them all out of there in just a few seconds.
There was plenty of time. He could have taken 5 at a time down the Beach 3 miles and came back for the rest. Earlier in the movie he was moving so fast men were falling from the sky at nearly the same time and he was teleporting them one at a time.

Stupidity: The prison where Magneto is held should have had a contingency plan just in case of escape, like machine guns outside the cell, or tranquilizer darts, or gas.
Suggested correction: What good would machine guns and tranquilizer darts be against a man who can literally control and manipulate metal? As for gas, the area outside the cell is so large that any gas would quickly dissipate before it could be effective.

Stupidity: This highly trained squad of soldiers is sent into a known contaminated zone with all manner of chaos going on within in...and the second one of them sees a woman outside his APC he ignores a direct order and pops outside to see how she's doing.

Stupidity: Joe's second homicide aims to be ruled as accidental death, but Joe's plan involves a furious struggle with the guy underwater, who claws and bites at his arm, as he applies pressure to his shoulder and neck. Moreover, their struggle happens close to the water surface but the bodyguard who is there does not hear or see anything. (00:35:00)

Stupidity: When Will Smith and Gene Hackman are running through the railroad yard. Gene calls Will by his real name, "Will" and not by his character's name "Robert."
Suggested correction: You could be a little bit more specific, but I don't hear him say "Will" at any point during that run.

Stupidity: Considering the movie takes place in the winter of '75, it seems unlikely that the babysitter would arrive in a halter top and barefeet.
Suggested correction: I agree that this is a "stupidity", but think your use of the words "it seems unlikely" allows for the suggested corrections already given. Perhaps replace "it seems unlikely" to "it isn't rational." Even if the daytime temperature was mild for winter, the temperature would probably drop by around 30° overnight.
Suggested correction: Actually, January of 1975 was very mild, much like the winter in the northeast this year, so it would not be impossible for the babysitter to wear unseasonable clothing.
Suggested correction: Ordinarily I would agree with this observation, however, I believe the girls outfit matches her carefree attitude. She did bong hits in the family bathroom, laid on the boys bed seductively and asked him if he French kissed so dressing comfortably to babysit isn't out of context.
Adding to this, almost every babysitter I had growing up went barefoot or at least shoeless. Even this past new years eve, the young lady who came to watch my kids took her shoes off as soon as she came in the house.
It is a common courtesy to remove shoes when entering someone's home to protect the carpeting (or other flooring) from getting soiled by whatever might be on the bottom of shoes after walking outdoors.
Maybe I'm wrong, but after watching this movie last night, it sounded like the girl was wearing flip-flops when she walked across the bathroom to open the door. Would it be rational for her to have worn sandals too?
Considering she was barefoot for most of the night, yes, she may have worn them for comfort.

Stupidity: Instead of breaking into Gordo's house, covering all the furniture in one room with sheets/thin blankets, and waiting for Gordo to return home in order to kill him via a "dramatic re-enactment" (in an adjacent room which was not shown to the audience), Bill could have taken Gordo anywhere to avoid getting caught or calling the police on himself. Had Bill taken Gordo to his already-"wrapped" motel room, he had enough injuries after the fight to claim self-defense against an intruder. (01:43:20)