Stupidity: To quietly kill the hotel valet he is replacing, Diabolik throws a knife at him from distance, hits him in the back, and then drags his body in the middle of the street to the nearest manhole, leaving a long streak of blood he does not conceal. If this sounds pretty risky and unsafe especially for a meticulously planned murder, you have also to consider that in the comic book from 1963 this movie otherwise faithfully adapts, Diabolik did nothing this foolish; he quietly killed the guy strangling him next to the spot he'd dump his body into.
Stupidity: Given Enchantress' power, why not just try to cure Dr June Moone, so she can't threaten the world? That's what the government should've done.
Suggested correction: We're talking about Amanda Waller who had no issues murdering innocent government employees that were accidentally exposed to her top-secret Suicide Squad program they weren't cleared for (versus making them sign an NDA not to talk about it as in a real-life accidental exposure to uncleared employees). Waller just took the easier option which was to threaten to kill Enchantress if she didn't obey versus spending countless dollars (and exposing more people to Waller's program) trying to cure her.
Stupidity: At the end of the movie during the shootout. Cops would not engage in automatic gun fire with dozens of civilians in direct cross fire. Why not get a chopper and chase them down a bit maybe in an open area with fewer civilians? Then maybe engage in gunfire.
Stupidity: In the flashback about the way the victim was poisoned, it would seem that the murderer straight out went to a waitress and handed them a single chalice of poisoned champagne, ordering the waitress to give that exact glass to the victim. That's just a little bit absurd; if it's a flashback based on a testimony, the case should have been solved in 0.1 minutes once the waitress says that that very well known person asked them to bring a glass to the victim - it's a request highly unusual and that would be easily remembered. If it's just some wild guess of the detective, that's a mighty strange way to imagine how things went, rather than just the killer slipping venom in the victim's glass when they were not looking. (01:04:00)
Stupidity: When Poirot's team attacks the Germans, they do it through the cover of gas they release. The Germans are having a good time chatting and not taking the situation seriously when there's a big cloud of noxious gas advancing towards them. Despite Poirot's oh-so-clever plan, they should by all means know that something is coming their way, but they get caught entirely with their pants down.
Stupidity: During the final shootout in Saint's club, Lincoln (the long-haired hitman) sneaks up on the Punisher and fires at his chest with a shotgun at point-blank range, which does not harm the Punisher because of his body armor. Even though Lincoln could see that the Punisher was wearing body armor, he takes another point-blank shot at his chest to no effect when he had a clear head shot.
Stupidity: Soon after the new art therapy instructor Anna arrived for her first day at the mental hospital, Leena - the most dangerous patient - was not in her room and nobody could find her. The hospital went into lock down and the doctor took Anna to a room. Without first looking in the room, the doctor said, "Do not leave this room. Don't worry, you will be safe here and we'll come back after we found her" and then locked Anna inside the room - with Leena. (00:03:36 - 00:04:41)
Stupidity: Patrizia Reggiani is no rocket scientist in this movie, but it's quite bizarre that calling the fortune-teller she sees on TV, with her name written in giant letters in two different spots on screen, she asks her "What's your name?" It makes sense for the international audience who may not recognize the word "Pina" as a name, but an Italian wouldn't have any doubt. (00:41:05)
Stupidity: The building is supposed to be without power - at all since the generator has been destroyed - and life support machines are not powered up, but the 3D printers in every room are powered up - so that the good guy can squish the bad guy's head in it, and the elevators, so that the good guys can escape. What sort of hospital has its electric grid rigged in a way that the elevators keep working but critical surgical equipment goes dead the moment the power fails? (01:12:00)
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: During the ghost chase montage, why would Velma look for her glasses with her hand in midair instead than on the ground? No matter how nearsighted you are, the closest wall, or obstacle, is meters away and you'll never find your glasses anywhere but the floor. She does it for a longer time than anyone would. (00:52:40)
Stupidity: One of the major reveals and plot twists of the movie lies in the fact that a certain character is an accomplice of the medium. The reveal, though, does not explain at all how said individual managed to fool Poirot; the trick briefly shown involves a simple rope pull to open a door. Poirot was looking exactly for that kind of trick, paces around the room constantly on maximum alert, and examines the door itself later. Likewise, it does not explain where and how they could hide the stuffed animal.
Stupidity: It's very idiotic that Michael and Karen kept the same security password, even after being harassed and not feeling comfortable with Pete being around them any longer. There's no way the pyramid password should have been kept the same, with Pete being able to enter their home, plant drugs, and frame Michael. Changing your security password, the same password that the lunatic cop once knew, would be the first thing to do after his psycho behavior starts.
Stupidity: The protagonist has a sophisticated alarm system with cameras...that do not properly show who is at the gates (the cameras are positioned in a way that does not show the face of the person ringing). The bad guys are disguised as police officers...and wear ski masks, which would have made the disguise entirely pointless - but luckily for them, Nicholas Cage can't operate cameras nor looked at the ones on the entryway or the front of the house, didn't open the door sooner nor peeps before opening. They could not know any of that, though, just that the camera at the entrance has a terrible angle.
Stupidity: Why does a safe house have a skylight? It is a secure building with hardened doors but a window in the roof?
Stupidity: The first time they see the bad guy in the Land Rover, Morgan has him in his sights but can't shoot, as he doesn't want to kill him. Clearly, the obvious thing to do is to shoot the car tires, but he doesn't and lets him drive off.
Suggested correction: Shooting out car tires is not an actual effective strategy to get a vehicle to stop. A 9mm bullet simply doesn't cause enough damage to a tire to get it to go flat immediately. It causes similar damage as running over a nail. It is a movie cliche, similar to using a gun to shoot out a lock or a rope, it just doesn't happen in real life.
Stupidity: The kidnappers steal a silver Citroen van and take it to a junkyard to switch the plates. They steal plates off an older green color Asian type sedan and place them on the van. If the cops run the plates as they normally do random checks as they drive, those plates will not match that vehicle. They should have found the same make and color of Citroen van they stole and swapped plates for plates, the chances of the owner noticing are small. Now if the plates get run they match that vehicle. (00:00:38 - 00:01:18)
Stupidity: When they raid the warehouse as the criminals are trying to leave town, they load the girls into.a white van. A man (Bruce Willis) wearing a ski mask gets out of the passenger side and covers with his pistol as they load the girls into the van. The entire time the slide on his weapon is back, so the gun is not ready to fire.
Stupidity: If Gabriel and his crew are such incredible hackers, why in the heck would they use a government vehicle that is LoJacked? Even so, wouldn't they be cognizant enough to disable the GPS tracker just in case?