Stupidity: After stealing the candy tin full of money, Joey gave it to Matt. Standing in front of the house, Matt opened the tin to see all the cash ($12,600). Joey asked him if anyone saw him, and Matt replied, "No. Let's go before they do." Instead of "hiding" the candy tin in his backpack, Matt carried the tin out in the open - and soon ran into a man wearing a security guard uniform.
Stupidity: The ending has a bit of a twist; apparently, octogenarian college professor Morgan Freeman somehow chased down and murdered offscreen 6'3" professional assassin Vernon Davis. That's not the toughest part to swallow, though; he also sent the two detectives (one of whom he is not even supposed to know of) via UPS 2-day delivery mail some body parts of his victim. We don't know which part Lavazzi gets (genitalia were mentioned earlier), but Boyd gets the eyes and decides to eat them. For starters, unrefrigerated 2-3 day old eyes would never look as pristine as the ones Boyd gets. Also, Morgan Freeman mentioned earlier in the movie that for the power of Muti to be effective, the body parts need to be taken from a victim that is alive, screaming, and eaten only mixed with herbs and other catalysts. So what the detective does doesn't make sense even in the movie lore.
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.
Stupidity: When Drake cuts off power to Hayes' apartment, the cops can't physically make a landlord abide by the laws, and seeing a judge would take months. In the meantime, by keeping the power off in the apartment, Hayes would have had no choice but to abandon his scheme and move on to another victim. With no power in the apartment, it's unusable and unlivable.
Stupidity: Considering the movie takes place in the winter of '75, it seems unlikely that the babysitter would arrive in a halter top and barefeet.
Suggested correction: I agree that this is a "stupidity", but think your use of the words "it seems unlikely" allows for the suggested corrections already given. Perhaps replace "it seems unlikely" to "it isn't rational." Even if the daytime temperature was mild for winter, the temperature would probably drop by around 30° overnight.
Suggested correction: Actually, January of 1975 was very mild, much like the winter in the northeast this year, so it would not be impossible for the babysitter to wear unseasonable clothing.
Suggested correction: Ordinarily I would agree with this observation, however, I believe the girls outfit matches her carefree attitude. She did bong hits in the family bathroom, laid on the boys bed seductively and asked him if he French kissed so dressing comfortably to babysit isn't out of context.
Adding to this, almost every babysitter I had growing up went barefoot or at least shoeless. Even this past new years eve, the young lady who came to watch my kids took her shoes off as soon as she came in the house.
It is a common courtesy to remove shoes when entering someone's home to protect the carpeting (or other flooring) from getting soiled by whatever might be on the bottom of shoes after walking outdoors.
Maybe I'm wrong, but after watching this movie last night, it sounded like the girl was wearing flip-flops when she walked across the bathroom to open the door. Would it be rational for her to have worn sandals too?
Considering she was barefoot for most of the night, yes, she may have worn them for comfort.
Stupidity: Crystal knows she is being hunted and in a very dangerous life-threatening situation yet, after she kills "Ma and Pops" in their Main Street Market, she grabs only a few shotgun shells out of the open box instead of taking all of them or as many as she could find. Also, she walks some distance to the store but did not take anything to drink or eat. (00:27:00 - 00:27:55)
Stupidity: Wes is characterized as one of the more careful characters early on, buying both a stun gun and pepper spray. When he comes home after the meeting where the dangers of Ghostface were further laid out, he proceeds to set both his weapons down and takes a shower after his mom tells him he'll be alone in the house, which is exactly how Tara and countless victims of previous sprees were attacked. The fact he even lived through his shower is lucky enough.
Stupidity: A detective who explicitly frequents morgues not being able to tell the difference between a real slashed throat and fake blood spurted on a neck is one thing. When he returns to the room and finds the body missing, instead of becoming alert, drawing his gun, putting his head on a swivel, and warning his friend outside, he slowly walks over to examine the razor and figure out how the magic trick was performed, allowing the killer to ambush and kill him almost comically easily.
Stupidity: Dahlia, fleeing her husband, asks Parker, "Well, where we [her and daughter Ashley] gonna go?" Parker replies, "I know a place where you can go" and takes them to Marcus' house, parking his car there. (Mikey and Louis are looking for his car and find it.) Parker, though recently fired, is/was a social worker. Social workers are among the professions that have the greatest awareness of available community resources. Parker should have taken them to a shelter or other safe place. (01:06:04)
Stupidity: Molly was being hunted and didn't know if she could trust Rayburn when he encountered her. Rayburn told Molly that he wanted to help, wouldn't hurt her, put a blanket around her, and even carried her in the woods for some distance. When he put her on the ground (along with his backpack and rifle) to go find the rope to open the pitfall doors and had his back turned, Molly got out from under the blanket and hid nearby. Rayburn quickly found Molly, and Molly made a lame attempt at attacking him with some kind of club. The next day when Rayburn and Molly were in Rayburn's house and her hunter showed up and attacked Rayburn, Molly grabbed Rayburn's rifle and fired several shots at the hunter. Molly obviously knew how to use a rifle, so it was asinine for her to have hidden from Rayburn the previously night without taking his rifle (or the blanket). (00:36:22)
Stupidity: When Amy tries to use the security cameras at Desi's house to make it look like he raped her, wouldn't the cops be curious as to why there was just one little scene - and not 30 days worth of footage? Wouldn't they question what happened to the rest of the footage (showing her being looked after by Desi and living comfortably), and why that little bit showing her crawling on the ground was left undeleted. Also she tied lace around her hands. Anyone could break material like that if they tried hard enough. Why would Desi risk that?
Stupidity: How did Elvis not know that Gary wasn't in his house? Gary said he just put 2 bullets in Elvis' poster. And why wouldn't his wife tell Elvis they weren't at home? And what happened to the cops who busted into his home and found nobody there? Why wouldn't they go to the station?
Stupidity: Noah chases one suspect while Leslie chases the other two. Noah eventually pulls out his gun and says, "Stop, police!" Leslie doesn't even try to draw her weapon until she hears sounds from the nearby brushes - but she barely has her hand on the holster when she turns around and gets punched in the face. Leslie is knocked over and the other man she was chasing repeatedly hits her in the face, quite hard. Her injuries could have been avoided simply by having her gun ready to aim and use. (01:04:48)