Stupidity: At the beauty pageant, Helen keeps screaming and looking at a precise point; however, nobody in the crowd ever looks towards that direction, even in passing. Humans don't behave that way. It could have been very easy to explain people at least glancing and not noticing anything because the stage lights were too bright and blinding them, but depriving every single person in the crowd of natural curiosity and survival instincts is just a little bit of a stretch.
Stupidity: Since the killer is not a supernatural monster, the powers of stealth he shows in the scene of the gym are absurd. Forgetting the fact that he snuck into the gym past the guard (it could have a back entrance we don't see), he opens Barry's locker and takes his stuff in seconds without making a sound. (00:40:00)
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."
