Stupidity: In the scene where Lewis and Clark nearly hit the Event Horizon, One of the crew is calling out the closing distance and another confirms this information. Regardless of clouds obscuring their view they were aware of their proximity and the fact that they were speeding towards it and forced to attempt an abrupt stop makes no sense.
Stupidity: Ghostface ambushes Sidney and her friend with the two detectives protecting her while in the car. Ghostface busts out of the driver window, and slashes the throat of the driver detective and then assaults his partner, kicking the crap out of him. Ghostface is obviously going with the intent to kill and has a weapon. He just killed one of the detectives and threw the other in the street in front of the car. When Ghostface jumps in the car to take off, the living detective, beaten, jumps up with his gun trained on Ghostface. But rather than do anything smart, he just yells at the killer, the cop killer, to freeze and get out of the running car that he's standing in front of. He just saw the guy kill his own partner and knows he is intending to kill the girls in the back. His gun is pointed at Ghostface who is about to drive over him, but he just yells at him instead of shooting.
Stupidity: When the teens are about dump Ben Willis off the pier, he regains consciousness and snatches Helen's crown. Despite knowing he's alive with strength to spare, they nonetheless drop him in the water and continually refer to him as "dead."
Stupidity: The first time they see the bad guy in the Land Rover, Morgan has him in his sights but can't shoot, as he doesn't want to kill him. Clearly, the obvious thing to do is to shoot the car tires, but he doesn't and lets him drive off.
Suggested correction: Shooting out car tires is not an actual effective strategy to get a vehicle to stop. A 9mm bullet simply doesn't cause enough damage to a tire to get it to go flat immediately. It causes similar damage as running over a nail. It is a movie cliche, similar to using a gun to shoot out a lock or a rope, it just doesn't happen in real life.
Stupidity: When White and Exley meet outside the motel and realise they've been set up, White suggests they leave, but Exley says it's too late. It wasn't even close to too late. There were no other people around, they had cars and there was a road right in front of them. Then they decide to go trap themselves inside the motel. It seems like they wanted to be shot.
Stupidity: Anyone with a job in the White House would have to be known to the Secret Service on a daily basis, so the two Secret Service agents that find Cory the janitor should have been aware of his identity without him having to state who he was and that he worked there.