Stupidity: When Roy finally gets to the Lima project in the shuttle but can't dock, he just lets it drift away - he could have at least tethered it to the station to use it for his return trip.
Suggested correction: There is no way to know the reason why he did this. It's plausible, or even likely, that the pod was out of fuel. Not only that, but it could not dock with Lima because it was damaged, so it's likely that the damage played into the decision as well.
Stupidity: While Tommy and Snake Eyes are trying to escape the docks in the truck, the Yakuza men surround the truck and stab over a dozen swords in all parts of the cab. Not one of the men ever thinks to use their sword to slash the tires, allowing the heroes to make an easy escape.
Stupidity: Oldboy finds the right Blue Dragon restaurant that the prison uses. But him running after the delivery boy doesn't make sense. How does he know the delivery boy is going to the prison? He knows it's the right takeaway, but that's all he knows. So, would he have a moped, bicycle, or car ready to use surely? The takeaway is a long way from the prison (as he says himself in narration), so he wouldn't just wait around for a moped delivery to run after, especially as a good chance he wouldn't be able to keep up.
Stupidity: When the saw yo-yo comes down for the third time, Bond grabs the cord to pull the wielder down off the gallery. That was, when you think about it, a patently bad idea. If the yo-yo hadn't become stuck in the desk, Bond would be collecting his fingers in his hat (note that the blades are still spinning as Bond grabs). (01:15:45)
Stupidity: When Bishop is first holding the gun on Gina in the cabin, he stands close enough for her to grab the gun and try to get it off him. A man of his experience would never make that mistake, it's one of the basic rules of controlling someone at gun point: Stand more than an arm's length away.
Stupidity: In 300 years, in an empoverished world full of people hungry for techs, nobody ever tried to remove the ship from a small pond barely 15 feet deep, and everything inside seems intact. It is mentioned that few tried because the technology is hard to sell being unknown (which is laughable), but surely some would try to strip the ship for alloys, and certainly the lights and monitors wouldn't stay untouched in a world based on scavenging. For 300 years and so close to the city, even.
Stupidity: The bodyguard takes Michael's pistol from him and later shoots the pistol near Michael's ear, deafening him, then beats him a bit and leaves him on the ground. As the bodyguard is walking away he gives Michael his sidearm back by ejecting the magazine and tossing the gun on Michael's body. He however didn't eject the bullet in the chamber. Michael's gun, a Sig Sauer, doesn't have a magazine disconnect which prevents a gun from firing with a magazine removed. This was a safety feature for police. (01:33:00 - 01:37:00)
Stupidity: Since the main people could not delete, or even change their own Facebook accounts; why not contact Facebook support in order for the company to do it for them?
Stupidity: At the very beginning of Donnie Yen's fight inside the CIA conference room, security barriers start descending in the room, windows first and then doors, but somehow the exitway for him (which even communicates with the main elevator. Not a secure bunker or anything) starts shutting down a minute later so he can baseball slide past it before it closes. That's pretty nonsensical security protocol. In fact, the whole operation is successful because apparently the CIA Headquarters lack any cameras and sensors in the corridors, security at the lower floors, main doors, perimeter, especially during the top brass meetings (that happen in a room with huge windows with reinforced glass a man can break jumping at it). (00:09:20)
Stupidity: When Stuntman Mike is taking photos of the girls, he is shooting with the lens cap on the camera.
Stupidity: When the army base gets overrun the girl jumps on a soldier and starts biting his neck. The woman soldier that's with him aims her gun at them but doesn't shoot, knowing full well there's no hope for the man. There is utter carnage going on all around them and instead she tries to help him and gets attacked in the same way. This could be a plot hole as well as the girl in question is the one that holds the key to survival.
Stupidity: For a brilliant criminal mastermind, Cyrus makes so many idiotic mistakes. (1) He leaves his entire escape plan hidden in the wall for the guards to find later instead of trying to dispose or destroy them (2) He makes the fatal mistake of trusting Santiago completely and never suspecting a double-cross. At the very least, he should have checked all of Lerner airfield just in case the plane was hiding (which it was). (3) He never notices or even questions Billy Bedlam's sudden absence until he sees his body. Odd considering he notice Santiago's absence immediately. And (4) When escaping on the firetruck, he (pointlessly) chooses to ride on the ladder instead of the front seat where he stands out, and Poe and Larkin both spot him. No surprise his whole plan failed.
Stupidity: The 1st time Foley enters the warehouse with the woman, 2 guys enter with the wooden box and black bags on top to transfer the bonds, then take it back to the truck. Why enter the warehouse at all when they could've put the bonds in the bag anyway, inside the van? They had no reason to go to the warehouse at all. (00:42:20 - 00:43:25)
Stupidity: The family ask 3 so-called ghost experts into the house. After seeing flying objects in the kids' room, they are suitably impressed. But later on, the female expert is sleeping, one of the men is in the kitchen wanting to cook a steak, and the second man has his back to the monitors, his head buried in a crossword puzzle and he has headphones on with music on, so he can't see, hear or see what is going on.
Suggested correction: The only one acting stupid in this scene is the guy at the monitors. They have to eat and sleep sometime; if anything, having two people awake and one asleep at a time is the cautious route. The one guy goes into the kitchen to cook a steak, but the guy at the monitors, despite being told he'll be the only one watching them, doesn't put down his drawing or take off his headphones, depriving him of sight and sound.
Stupidity: There's no reason whatsoever for Mr. Walker to trash the other rooms of David's partners. Someone as tough-minded as Mr. Walker would have been able to recognize the consequences of his behavior. He could have simply trashed David's room and let it be. It simply seems like a plot device to justify David's gang attacking the Walker residence.