Stupidity: Alex, a contract killer, went to the hospital to kill a patient. After parking in the hospital garage, Alex put his car keys under the sun visor, risking the possibility that his car could be stolen. When Alex returned to his vehicle, the keys were not there. A professional or expert assassin should take precautions to assure his getaway car will be there and keep his keys on him. (00:01:45 - 00:04:30)
Stupidity: To save the people from rubble falling on their heads Flash does not move them aside like he did with his future love, but does some strange manoeuvre which takes seconds - since we see people moving normally - and happens in midair (how does he get there?) and that does not take care of a huge chunk of concrete which he does nothing about, shouting just "No!", but Cyborg has all the time he needs to load his Mega Man arm and vaporize it in midair. (02:00:00)
Stupidity: The whole movie happens for unbelievably convoluted causes. Despite their friendship and the simple fact that he still runs an occult shop (showing that he's not exactly insensitive to the past), Ray in years never spent a single moment to check on Egon's whereabouts, which he knew, or listen to him. The city has Shandor's name all over and any cursory investigation would have unveiled the connection. Assuming of course that Egon turned into such a lunatic he couldn't do the namedropping himself.
Stupidity: When the rebel leader talks to Rick Flag guaranteeing her help, she mentions that she will help to find "this Gaius Grieves", speaking as if it was someone unknown to her. He's been around the island (going to bars and surely not being reclusive) for 30 years; it's pretty difficult to think it would not be one of the most known people on the island, given his role, unique appearance and the small community.
Stupidity: The ship crashes at the end after the reverse polarity from the shuttle causes an explosion. This could have been avoided by a) doing a spacewalk with a multimeter and checking the connections or b) not connecting the shuttle to the mothership. And it is hard to believe that there were no circuit breakers or fuses that would blow and protect the ship.
Stupidity: There was no particular reason for Nuclear Man to take Lacy into the space in the first place.
Stupidity: When Matt goes to the bank to close out the account he learns that it's been closed already by Kelly. Matt says he will be expelled, but he never did anything wrong except lie about who Kelly was. The bank teller is the one who was flirting with him and gave him the money with out any proper ID or papers, so if anything the bank would reimburse Matt/the school.
Stupidity: When they are preparing for a German assault towards the end of the movie, Miller explains to them the concept of the sticky bomb and adds, "If you have a better idea of knocking the treads off a tank I'd like to hear it." Um... The bazooka? They had eight rounds for it, and it could have easily been used to disable the treads. And the men wouldn't blow themselves up with it. While it couldn't destroy a tank by penetrating the armour, it's certainly strong enough to disable the tracks.
Suggested correction: Allied forces familiar with the Panzer VI "Tiger", a 60-ton Main Battle Tank during the war knew that the armor is very tough and, even with support fire from a friendly tank, the odds of destroying a Tiger tank with a bazooka like Horvath's are pretty small. From the infantry perspective, techniques that were developed and employed in order to combat heavy Tiger tanks focused mainly on disabling the tank rather than destroying it. Anti-tank weapons of the era, such as the bazooka, were ineffective against most areas of the Tiger's armor, so specific weak points in the design were the focus. Hitting the Tiger in the tracks, suspension, engine compartment, observation slits, and in the joint between the main body and turret were some of the common weak points. Tiger tanks could only be destroyed head-on or from the sides by land mines, or direct hits by heavy artillery shells, or bombs dropped from aircraft. In the film, the first Tiger is disabled by taking out the tracks with "sticky bombs" followed by grenades thrown in the turret hatch. When Horvath fires at the second Tiger, both shots are placed on the joint between the body and the turret, the idea most likely being to hinder or incapacitate the turret's ability to swivel left or right. As the war went on, the Allies developed better strategies for disabling Tigers. One example involved British Cromwell or US Sherman tanks trying to "flank" a Tiger by working in squadrons or columns. One or more tanks would act as a diversion to keep the Tiger's crew focused in front of it while another tank would maneuver behind the Tiger and hit it in the rear section where its armor was the weakest.
Stupidity: Captain Poison has a fairly good idea of where Solomon buried the diamond. We know this since when he leads the captured Solomon to the spot, there are already several holes dug looking for it. Despite knowing roughly where the diamond is - down to a relatively small area - he makes no serious effort to excavate the ground, instead contenting himself with a handful of incredibly shallow holes.
Stupidity: Knowing that the Klowns' noses are their weak point from previously shooting them, Dave doesn't bother to shoot the giant Klown at the end with his pistol, instead waiting to be almost crushed and finally popping it with his badge pin.
Stupidity: Why did the bad guys even go for Xander as he was snowboarding down the mountainside? First of all, it was impossible for them to even get to him as the mountainside had several cliffs. Secondly, why did so many go? Wouldn't it be clever to have as few as possible leave in case his snowboarding was simply to draw attention away from an ambush? They knew he was an agent by now and should know he could have gotten reinforcements. Thirdly, they could just have simply waited for him to get to them.
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: Zoe and her team go into the medical university to get medical supplies for their camp and Lily. As they are leaving, Zoe sees the Epidemiology room where she used to work and waits, letting her team run off leaving her behind and then goes into the room alone so she can get pictures and some small bottles. Letting her team run off leaving her by herself in a zombie infested building in a city without telling her team that she's not following them. And this did lead to her having to shoot at a zombie that jumped her, alerting the other zombies around, and is what got Frank killed and lead to the smart zombie stowing away on their Hummers and sneaking into their camp. (00:29:35)
Stupidity: The bad guy who spies on Bosley is visible from the very beginning of the scene, when Elena is not even inside the cafe yet. The cafe does not have many customers and the bad guy is using a loud vintage typewriter with a big mirror mounted on top (!). The Angels are portrayed as being super smart and their setup is so careful, but somehow they managed to miss something amazingly obvious. Conversely, nobody would have ever paid attention to a laptop or any silent, modern-age device perhaps with a camera or something similar, so the bad guy chose the most blatantly conspicuous accoutrement for his spying job. Try showing up to a cafe punching the keys of a big clunky typewriter and literally everyone will be looking at you. (00:18:25)
Stupidity: The guy who offered to help Rachel go to her car at the gas station and get away from road-raging Tom walked directly in front of the path Tom would be taking to leave. When the guy realised Tom was going to run him over, he went onto the road instead of toward the store where he would be safer. Also, the guy - knowing Rachel's situation - foolishly told Tom that he got his plate number, which served to aggravate Tom into driving into him. (00:32:15)
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: In the opening scene, when Jason lunges at Whitney, the screen cuts to the title card with his machete swinging 12-6 just inches from her skull. This makes it hard to believe he had a change of heart and pulled his windup before splitting her head in half.