Stupidity: Peter Parker watches Richard Parker's last message, the upload he did on the plane to his super encrypted server. As he does that, the interface used is one of a mail and there's even the sender; "Rich-Park@oscorp.web." So Richard Parker sent his dying message he wanted to keep from the evil corporation...through his evil corporate mail account, and to an account that contains the location of his secret lab, "Roosevelt." (01:32:50)
Stupidity: Robocop is just about to be unveiled to the press for the first time, and they decide right beforehand is the perfect time to upload a massive amount of data, including his own attempted murder. Then, they seem shocked when that causes problems. No reason to do that right before a very public, time-sensitive moment except for the sake of the plot.
Stupidity: The creatures in the maze make it inside the living area after the gates open and some of the heroes hide in the corn field. While that alone isn't the smartest thing... one of them keeps a lit torch in their hand burning brightly at night while trying to hide from these creatures.
Stupidity: When he's using carbon monoxide to poison the corrupt detective Frank Masters, the windows in the car were operated by the key fob. Unusual, but OK. Maybe. But the detective could've simply opened the doors after McCaul left him in there. The door worked when he was forced into the car. (01:24:30)
Stupidity: If Leo wants to kill his son's killer at any cost and no matter what happens, he should've gone directly to his House when the purge starts.
Suggested correction: He absolutely is headed there, but we see at least one incident where his path is blocked due to people out purging, and he needs to turn around. That detour caused him to go a different route, which led him to the mother and daughter. We even see him struggling with the decision on whether or not to help them. He decides to do so, and the rest of the movie unfolds as we see, but there is no mistake.
Stupidity: In the exciting denouement when the SS company approach the ostensibly disabled Sherman, the SS would have just walked around it. A burning tank was a common occurrence. I doubt they would start climbing on it and they certainly wouldn't start charging at it individually as to get mowed down. The SS were well trained units. Such stupidity is unlikely.
Stupidity: Four H.S. seniors are sitting in an SUV. A storm quickly intensifies and Billy gets out of the back seat to get a better look (wipers are on "fast"). Seconds later, Billy spots a tornado coming. Marcia (driver) tells Billy to "get in." Needing to flee the fast-approaching tornado, Marcia wants to leave as soon as Billy is in the SUV, so she yells, "Billy, get in!" The tornado is feet away when Billy closes the door - whew, he's safe! Marcia STARTS the SUV when the tornado starts bashing it. (00:01:14 - 00:01:38)