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: Why would they drive all the way to Marylebone Railway Station in central London when Southbury Road station is only a thirty-second drive away?
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: The chef/cook of the house has his rifle, and he knows Morgan lost control and pretty much killed everybody on the premises. He comes face to face with her, but he lowers his rifle instead of taking the subject (Morgan) out with a shot. There is no logic here but to only pro-long the film. There's no reasoning with a scientifically created subject which is killing everybody it comes into contact with. (01:09:00)
Stupidity: Nicholas Cage saves the kids coming out of the dark dimension exactly at midnight but gets back home at dawn. It should be noted that he has two other kids to bring back home and if we assume he did that already, it would explain part of the time discrepancy. In that case he kept his wife up all night when she was fearing for the safety of both without a word, but she's not upset or anything.