Stupidity: When Governor Swann is trying to encourage his daughter while she's locked within the ship's chambers trying to escape, she climbs down to a boat. Nobody in the Navy would have left a boat there, neither would Jack (and why would he, especially without anyone noticing?). The boat just mysteriously appears to help her escape.
Stupidity: Even though Hermione reminds them that they must not be seen after freeing Buckbeak, they fly toward the castle, whooping and cheering because they're flying. Then, they land in the courtyard of the castle, have a conversation, and then Sirius flies off with Buckbeak. Not the behavior of trying to remain unseen and unheard.
Stupidity: The whole movie necessarily has to be filled with stupidity (we're talking about a 9 months kid besting 3 adults), but there's one part perhaps not so obvious and that may be related to a mistake about the ransom note. When the bad guys watch the news, it's obvious that their original plan failed, since they cannot retrieve the money at the designed drop zone, the police have been called and they'd need to rethink the whole operation. Yet they make no comment about it and don't seem bothered by that at all.
Stupidity: The highly trained commandos who knew everything about the NSA base and penetrated it during a perfectly planned operation through weapons and devices that pierce steel like butter, decided to stand outside the barn (so they knew something valuable was there) and its wooden door. It even has a direct line to the command center.
Stupidity: When the plane crashes and the family ducks into the small room off the main basement, powerful flames shoot all the way across the basement, up to the door that Ray closes just in time, but when he later opens it, nothing has burned, nothing is smouldering, not even fabric or paper, but the walls are scarred... as if from fire. (00:40:40)
Stupidity: During the gun battles with the "Tropic Thunder" actors, not one of the Flaming Dragon soldiers notice there is something strange about how the actors are firing their weapons (i.e, in the air, over the heads of the Flaming Dragons, etc.) or that there is no damage inflicted when the actors are shooting at or near objects in the area. Those two factors alone would tip off the Flaming Dragons that blanks were being used in the weapons of the actors.
Stupidity: When Harry finds the Sword of Gryffindor at the bottom of the frozen pond, he breaks a man-sized hole in the ice, then strips down and jumps in. He could have broken a far larger hole in the ice, negating the risk of being unable to locate the hole upon coming back up. But because he doesn't, he nearly drowns when the locket resists and he can't surface (he couldn't have anticipated the locket's resistance, but that such a small hole would be hard to get out through was easily foreseeable.)
Stupidity: Spoiler alert. After the son makes it out, he could get a rescue team to get his dad by going in where he came out.
Stupidity: First, the hunter ties Benji with a nearly 10-metre-long rope - how did he expect that the dog wouldn't trash his place like that? Second, after the wolf attack, he simply unties Benji and puts him right next to the tied bird, serving the dog the chance to grab and escape with it on a silver platter.
Stupidity: Immediately after Unkar Plutt makes Rey a generous offer for BB-8 and she refuses, he tells someone over his communicator to follow her and bring back the droid. He should have at least waited until she was out of earshot before he said that, especially if he was trying to be covert about it.
Suggested correction: But he was out of earshot of her.
I posted this immediately after watching the scene in question, and it looked as though Plutt spoke into his communicator right after Rey turned around and went on her way; certainly too soon for her to have gotten more than a few steps away. Also, he spoke at a normal, conversational volume rather than anything that sounded like a whisper or "sotto voce", so unless he was relying on the ambient noise of other nearby activity, I still believe this "stupidity" is valid.
That depends on how sneaky you think Plutt is. Rey walks away in quick paces, so she is out of earshot. Also I don't think it bothers him that much if she heard, she is just a scavenger, what can she do about it?
Rey was definitely out of earshot. Rey walks completely out of the shot, which appears to be about 10 feet away. Unkar Plutt then angrily swipes the portions off the counter and picks up his communicator. At the pace Rey was walking she would have been a considerable distance away from him when he spoke. In addition, Unkar Plutt lowered his voice when he spoke because he was being sneaky. She might have been able to hear him speak, but it is totally reasonable that she wouldn't be close enough to make out exactly what he was saying.
Stupidity: Very soon after Damon is stranded, one of the many satellites around Mars inevitably picks up the fact that he has moved various objects around his site, indicating that he's still alive. Yet it never occurs to him that this would obviously, eventually happen. In which case, his best option would be to simply spell out a message with debris and stay put instead of planning some 50-day journey.
Stupidity: At the end of the plane chase Bond fails to finish off Hinx. Regardless whether he thinks he's dead or not, with a licence to kill he should have made sure.
Stupidity: Unless Snow has solid proof like pictures or video why should Katniss believe her main enemy's word that it was Alma Coin, not him, who killed those kids?
Suggested correction: This is a question and not a stupidity. Katniss didn't just accept Snow at his word. Earlier Gale had mentioned an attack strategy to inflict maximum casualties on medics that matched the attack on the Capitol. Then Gale could not deny his part in Prim's death. All the evidence pointed to Coin being responsible as Snow suggested.
I appreciate responses here because it means you're reading stuff and that makes my day.
Stupidity: In a flashback scene, a mother, father and daughter are taking pictures of Norm and two other polar bears. The daughter decides to run up to the three polar bears, but the parents appear to do nothing about it. The polar bears could have been a threat to their daughter for all they knew. (00:04:25)
Stupidity: Darren could have easily grabbed Ben out of the locker he climbed into by just pulling. Instead, he pushes it inward, causing it to close and allowing Ben to either hold onto it on the inside or lock the locker itself.