Stupidity: When Ruth goes to see Madame Arcati, after Elvira has arrived, the kettle on a gas two-burner hotplate is whistling, so Madame Arcati takes the whistle off the kettle and then the kettle off the hotplate and pours most of the water into a teapot, but, what is stupid is, she puts the kettle back onto the same burner without turning the gas off and in less than a minute the water is boiling its head off but they don't notice because the whistle is on the table and not where it is supposed to be, on the kettle.
Stupidity: Central to the plot is the layout of the Mars lander. There are no seats or any restraints of any kind in the lander, which is ridiculous. Spacecraft require safety belts in order to prevent astronauts from being injured during rapid course corrections. Additionally, ordinary rolling desk chairs would not be sent into space, and would certainly not be placed on a landing vehicle.
Stupidity: During the film's climax where Santa and his reindeer successfully ascend over Manhattan, the sleigh's rocket engine falls off and apparently is no longer needed. Isn't it rather risky (and foolish) to assume (or hope) that the other cities on his flight path have enough "belief power" to sustain him aloft for the rest of his journey?
Stupidity: Bridget car keys are lying on the shelves (again) after she has left her bags at the ATM. I suppose they could have taken her car after all when she and Mark try to think of a way to get to the hospital.
Stupidity: At the end of "You're Welcome", Maui puts Moana in a cave and placed a large rock blocking the only known exit. This means, as far as Maui knows, he's trapped a human in a cave with no food, water or exit as he didn't know Moana could make a very lucky escape. Basically Maui was going to leave Moana to starve to death so he could take her boat.
Suggested correction: This isn't a mistake. Maui doesn't care about anything other than escaping at this point. He even says, Without his hook he is nothing. He's not interested in returning the heart at first so even though he is a demigod, he has lost interest in being good. Another example is when he leaves Moana to face TeKa on her own.
Stupidity: Why would Stanley say the shoes fell out of the sky? It happened under a bridge. Any normal person would instantly realise someone threw them off the bridge.
Suggested correction: It's an idiom/expression. When something turns up out of nowhere, we say "it came/fell from the sky." In fact, Mr. Sir says this to Stanley when he finds Stanley with his empty bag of sunflower seeds, "Where did this come from? Did it fall from the sky?" Obviously a sarcastic way of saying, "it didn't get there by itself, someone put it there." So the shoes obviously fell from the bridge and Stanley knows this because Zero refers to the bridge later in the movie.
Stupidity: When Bobbi Jo sees Ash's severed possessed hand holding her hand, she freaks out and runs out of the cabin and then gets killed by possessed trees. While it's certainly natural for her to be terrified, why would she run AWAY from where all her friends are and go off by herself?
Suggested correction: She is a civilian in a blind panic, and even people with actual training have done dumber in panics (e.g., choking firefighters run away from other firefighters who could help them). She also has no idea how dangerous the woods are at this point; she walked to the cabin just fine and only saw scary things inside it, so she thinks she'll be fine if she just runs from the cabin.
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: It's mostly a fun absurdity, but it is somewhat contradictory to showcase the Ghostbusters being featured as the cover story of every major publication and news outlet, and yet to get help not only they put an ad on the newspaper, but a single person applies for the job (which is all it took for them to accept).
Stupidity: When Bob is fighting one of the Russians, Tatiana could have kidnapped Nota but instead stands beside her and watches. (00:52:05)
Stupidity: Long after the Marine Life Institute has closed for the night, the recording of Sigourney Weaver welcoming visitors is still playing.