Stupidity: Lecter fires the first bullet to alert the police that something is up, and the lift goes up, then comes down. Now in all this, only 6 or 7 go up the floor where Lecter was. Why aren't police sent in groups to investigate every floor? Lecter could have been anywhere, instead there are about 30 police huddled on the lobby floor.
Stupidity: When Laura goes back to the house to get her bag, she takes off her wedding ring and flushes it. Problem is, she knows how her husband is and doesn't take the time to make sure the ring goes down! But she makes sure there's no other trace of her being there (flushing her hair down the toilet and drying the floor off from her wet feet!).
Stupidity: When Ricky's girlfriend awakens inside the drug dealer's apartment, she runs off as soon as she realises what danger she is in. She runs through the apartment building, up the stairs to the roof and then commits suicide by jumping off the roof. Apparently, when she was running up the stairs, she never considered trying to escape the building or see if there was anyway of getting downstairs. (01:11:15)
Stupidity: Given Louise's character, it makes no sense at all for her to leave Thelma in charge of the money. She's known Thelma for years, and knows fully well how flaky Thelma is. And Louise is shown as a person who lives by "If you want something right, you've gotta do it yourself". She's responsible, perhaps even uptight, at that point in the movie. So it defies everything about her character that she would let Thelma guard the money - it smells like a device set up just to allow the money to be stolen.
Stupidity: The crack house workers are all topless to prevent 'hiding' any product for personal use. Yet are also wearing parachute type pants that they could easily hide things in.