Stupidity: When Susan is on the balcony with the man trying to kill her, she pulls out her gun with one hand (she's leaning on the other hand). He says she won't shoot because the gun's magazine has fallen out and Susan gives up and drops the gun. However, if there is a round in the chamber, the gun can still fire without a magazine in it. As trained as Susan is suppose to be, she should know this. But, if there's not a round in the chamber, then, as a trained agent, Susan is ineptly prepared to use her gun. If there's not a round in the chamber, pulling the trigger will not fire the gun nor will pulling the trigger chamber a round. But she would need both hands to chamber a round and she only has one hand free. There is the occasional gun that has a magazine disconnect safety, but it would be stupid for field agents to have one since they may be in a situation where they need to fire without a magazine in (such as this situation).
Stupidity: Howard has the opportunity to shoot Jack at the end, but doesn't for no discernable reason; he's already committed multiple felonies, and shooting Jack would help cover his tracks all the better. In fact, he could even have just taken the cash onto the subway and left Annie behind while staying in full disguise as a cop.
Suggested correction: Howard Payne's taunting dialogue in the subway station suggests that he wants Jack to live a long life, tormented by the fact Payne was able to beat him. He doesn't become intent on murdering Jack until the dye pack goes off, ruining the money. After that, he tries to shoot Jack but runs out of bullets, then decides to beat him to death with the detonator but fails.
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: In the opening scene with the military convoy, the two soldiers in the lead vehicle never notice the car veer into their lane, even though their faces are bathed in bright light from the car's headlights. They simply ignore it and keep talking to one another.
Stupidity: After stealing the taxi, Cassandra removes the license plate, and yet the taxi's identification number is located in bold plain sight on the doors and roof light.
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: Kord Headquarters goes into "lockdown" after the Scarab is stolen, which in this building, apparently means allowing all the guests to leave.
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: 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: The whole premise of the plan is summarized by Helen in the sentence "They don't know Andi is dead, so why would they suspect anything?" However, "they" conspired in unison to financially ruin her sister, and "they" did not answer the mail, none of them. The possibility that "they" all could have gathered and silenced her by force is one of the most likely ones, and yet neither she or Blanc consider even for a moment that the literal crime conspirators could have conspired.
Stupidity: The train which takes M from New York to London arrives looking like an old tube train, then when she's on board converts into a high-tech train, to her amazement, and whisks her across the Atlantic. Except...why did it ever look like a regular train? She's in a MIB station, it's only used by agents and aliens, it goes to another MIB station, and when it arrives and people get off / on before it continues its journey, it stays in its high-tech form anyway.
Stupidity: (SPOILERS) Despite knowing that Rowena killed the last person who was blackmailing her, Miles tries to use her secret to blackmail her into sleeping with him. Did he really believe that she wouldn't react with such drastic measures like she did before?
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: As Powell was standing at the completely wrong "eye" in the temple to begin with, all Lara had to do was say nothing of his mistake, he'd never had got the first piece of the triangle to begin with, world safe for another 5000 years.
