Stupidity: The heroines guess the plan of the villain with a thought process that can only be explained by the fact that they read the movie script. There is no way for them to surmise that the attack on the Skrull base, perpetrated under subterfuge, was intended to "syphon away the atmosphere", and not just the usage of a really powerful weapon. Even assuming that Kamala's objection to this particular point ("they could have just invaded or used a bomb") is a logical explanation that would disqualify without a second thought the fact that a Kree warlord would use a terrifying and cost-free weapon that is also a symbol of Kree's culture just for its power, and so that it makes sense that the heroines just instantly commit to an alternative theory, there's still a leap of logic in assuming the exact next step for the Kree's quest on revitalizing their homeland (which incidentally involves randomly dumping out of the blue a gigantic quantity of salt water on a densely populated planet).
Stupidity: The protagonist is wearing normal boots atop a spacesuit while being on a moon mission. (01:37:11)
Stupidity: Stitch wakes up in a kennel with dogs at the animal shelter. When Lilo picks him out and they walk out of the kennel, the lady freaks out and tells Nani, "We thought it was dead, it was hit by a truck!" So, what was thought to be a dead dog was put into a kennel with other living dogs. Think about that for a second. (00:24:54)
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.
Stupidity: When the policeman comes for the girls, the people run along a straight path, completely straight, without bothering to go over the fence right next to them or run in a different direction.
Stupidity: After making love, Selina notices Batman's scars. She surely was caught in the moment, but, it's something she really was bound to notice sooner. (00:53:10)
Suggested correction: She notices the scars on his back first, which are the worst of those on his body, this may well be the first time she sees his back.
Stupidity: The "keep everyone in the stadium" plan is foiled when gold is scattered around the outside and everyone leaves. The bad guys didn't consider locking the doors? Not least because once the terrifying sky tendrils descend and boiling red clouds start filling the arena, surely people would have started bolting for the wide open exits.