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: Simi sets the wooden tepee structure on fire with Claudia next to it, and Claudia's clothes get engulfed in flames. Claudia continues to stand next to the fire, flailing her arms instead of following the commonly-known "learn not to burn" procedure that is taught to children: "Stop, drop, and roll" to extinguish the fire on one's clothes - and to stay away from fire. (01:31:00)
Stupidity: At the police station, a bucket of tools was left along the wall within a couple inches of the jail cell door where so-called "Amityville Strangler" Joe Gallo was detained. Gallo was able to reach the tools, use something to unlock his cell, and have a weapon - sledgehammer - "to go." (00:46:57 - 00:57:30)
Stupidity: The cleaning crew can't open doors and stand in front of a large window. They see a couple walking a dog, so they scream, "Hey!" and wave their hands in the air, even though the people are not looking their way. They do not bang on the glass or use their flashlights to try to draw attention. (00:29:13)
Stupidity: When Michael is heading to the hospital and he just learns that the Cloverfield Station is gone, the whole scene of him driving is super unreal. It looks like he's not even driving, like it's a self-driving car or something because the steering wheel doesn't move at all while he's driving, and he isn't looking at the road (staring into space). The whole scene just doesn't feel realistic. (00:43:48 - 00:44:30)
Stupidity: Grace (?) came out of hiding holding a fire extinguisher upside-down as though prepared to use the fire extinguisher to whack any Allosaurus that approached her. Actually spraying the dinosaur's eyes with the chemical contents of the fire extinguisher - and from a greater distance by using the hose - would have been much more practical and effective as a repellent and thereby less likely to result in getting maimed/killed. (She did not use the fire extinguisher at all). (01:02:20)
Stupidity: After Danny kills Kat on the sidewalk, he just stands there with Rory while the other gang members flee to their vehicles. William comes running out of the Mexican restaurant and Rory tells Danny, "We gotta go, brother. Now." Rory sees William and gets into the vehicle without getting Danny to go with him. The gang drives away with Rory watching out the window as William tackles and fights with Danny. Rory and the rest of the violent gang left behind someone who just passed the initiation. (00:07:10 - 00:07:40)
Stupidity: Throughout the movie, and especially up on the top of the apartment building before they get rescued at the beginning of the movie, Gerry counts 12 seconds to check if someone has been infected. Just to mention this apartment example, he gets blood on his face and spends more than 12 seconds getting up and to the edge of the roof, plenty of time to become "Zeke." He then counts 12 seconds, as if they would actually matter to his infection.
Stupidity: When Joey is trying to escape from the Cenobites, she bumps into a man who calls her "Baby" and wonders where she's off to in such a hurry, possibly because he's looking for a booty call. The streets are literally on fire (there's a huge flame right next to the man) and buildings are exploding. Even if he's extremely horny, he should still be able to tell a woman doesn't want to stay around with so much chaos and destruction happening around them.
Suggested correction: The dude was probably high on various types of drugs and probably didn't even know where he was. Just a thought.
Too high to recognize buildings exploding and fires bursting from out of nowhere, but not too high to recognize a woman in distress?
He didn't recognize much did he? Well, he saw she was female. But not really what was going on.
He recognized she was off somewhere in a hurry. He also had a pretty instant reaction to seeing the Camerahead Cenobite.
Stupidity: In the opening scene, Sonny has come to her now-deceased father's house. Police and the coroner are in the basement taking notes while standing around the body - which is face down and awkwardly lying at the bottom of the steps. Det. Sabatino informed Sonny that the death was ruled accidental due to a high blood-alcohol level. Detectives or the coroner did not rule out other possibilities: natural cause, suicide, or murder. High blood-alcohol level could be secondary.
Stupidity: When one of Vincent Price's protege's leaves a wax work-in-progress, he doesn't cover it with a lightly damp cloth, which is very important: wax uncovered will go hard and useless.
Stupidity: A zombie is climbing up the apartment wall and is almost at Aidan's balcony railing. Instead of trying to push the Zombie off while he had the advantage (and there was a surfboard on the balcony that could have been used), Aidan ran inside and locked the door to the balcony. This furthered the plot and added excitement by having zombies coming at Aidan from multiple directions. (00:43:09)
Stupidity: After Caleb escapes the vampire "family" with his father and sister, he undergoes a blood transfusion which cures his vampirism. As soon as this was done Caleb, his father and sister should have fled somewhere else immediately. The vampire "family" knew where he lived as they kidnapped him in front of his home. Instead, they stick around the home, with no obvious intention of leaving. Of course, the vampires track them down and kidnap Sarah.
Stupidity: The murder during the opening scene is ridiculous. Angela chases a screaming woman down an alleyway, in broad daylight, in front of crowds of witnesses, while driving a truck, runs her over, then throws her body in the back of the truck and then waits right next to the alley where she murdered the girl to be picked up by the van headed to the camp. At no point did any one of the numerous people on the street try to help the girl or even just investigate the alley to see if she was hurt (supposing it was an accident) or just call the police?
Stupidity: Two oil rig workers were looking at two young ladies in bikinis who were sunning themselves on a boat/yacht. One oil rig worker said, "That's where we should be right now. With them, enjoying the sun, instead of baking in it." Both men had double layers on - a jacket or sweater over a jersey or T-shirt - and one man was wearing a tossel cap. Even if it gets cold on the rigs at night, they did not need to be dressed in warm attire during the sunny daylight hours. (00:10:35)