Stupidity: It is pretty silly for Martin Lawrence to go undercover as a police officer when it would make way more sense to go undercover as a janitor/custodian since his main goal is to gain access to the vent. A janitor would be a way less conspicuous disguise than a detective and slipping through a backdoor entrance disguised as a janitor should not be all that complicated for someone as savvy as Myles. But of course this would make a far less entertaining film.
Stupidity: After hearing the question on the radio station to win the Turbo Man doll and a failed attempt at the pay phone to answer it, Howard and Myron end up running two blocks to the station to answer the question. This is really stupid because the prize was going to the first caller with the answer and in the few min it would take to run to the station two blocks away and finally reach the DJ, many calls would have come in and most likely someone would have won already, way before the men arrived there.
Suggested correction: This isn't a stupidity or a mistake. What else did you expect them to do? Plus, the DJ even later asks if they expected him to actually have a Turbo Doll in the studio, and they both said "yes."
Not only that but, Myron had ripped the phone receiver out so Howard couldn't give the answer to the DJ. Howard and Myron running to the radio station was the only other option they had. At that point, it would only be a matter of if they got to the station in time before somebody could call in with the right answer.
It was a very easy question naming santa's reindeer. Although some people may not quite know them all... most people do. Now if it was a relatively hard question, our two guys probably had a better chance. But all good points made here in all these comments.
Stupidity: When Dr. James Harvey dies, there should be a body left behind in the manhole. After Kat and Casper revive him in his ghost form in the Lazarus, he comes out with a body (and clothing). One can assume that there are now two bodies of him, one alive and one dead. That would make an interesting article in the newspapers of the next day.
Stupidity: The fact that Nolte even gives in to Eddie's demands is ridiculous. Why not just interview him in prison, ask him where to look for certain people, etc, and if it's a dead end, report back and ask for further tips, etc. They had zero problem going to prison and asking Kirkland Smith in the sequel.
Suggested correction: He refused to tell him anything unless Kates takes him out of prison.
Stupidity: The protagonists need to know what Pope is planning with his drug shipments, in secret. So they sneak under a false name into Pope's party and... the policewoman goes dancing with Pope, who knows her and that she is a police officer! Good that nobody asks her anything - she'd have no way to explain her presence! At no point it is even hinted that he was just about to go upstairs, why would he, after all, with all those guests? And their secret mission continues with the alarm being triggered and Ice Cube KTFOing guards. Some stealthy mission, and they are even captured at the end! And even after all these epic fails, they just assume that Pope is not going to change anything about the shipment details. And to make all of this even worse, they know about the port commissioner situation, they talk about it and how necessary it is for Pope to control the commissioner, but don't take half a second to mention his name, which is all it takes for AJ later in the movie to 'remember' that he's been bribed.
Stupidity: When Gail shoos Luke off the first day, in fact nobody accompanies him to the door and they discuss the evil plans when he's not even gone nor they even check he is, they just go ahead with the script. It's a rather odd dynamic, very rushed and movie logic-like. Or theater logic, since it's a typical 'exit stage left' moment.
Stupidity: During the ghost chase montage, why would Velma look for her glasses with her hand in midair instead than on the ground? No matter how nearsighted you are, the closest wall, or obstacle, is meters away and you'll never find your glasses anywhere but the floor. She does it for a longer time than anyone would. (00:52:40)
Stupidity: The Joneses forget to change their New York license plates to Georgia ones as part of their cover.
Stupidity: Rescuing Manfred and Diego from the giant carnivorous plant, Buck could have cut both wires simultaneously to avoid that unnecessary horrible potential outcome of cutting the wrong one. The wires were stretchable enough for them to have been held together to then get cut at the same time. (00:37:40)
Suggested correction: Cutting both wires simultaneously would probably cause a different effect. Besides, Buck isn't very intelligent.
Stupidity: When Claude was leaving with the doll, he called the Good Boys "fools" and said he would have paid $1,000. The Good Boys knew how to use the internet to find out the value of the Ascension card [Turzan of Uzkara] and the price for a new drone but didn't think of looking up the cost of a CPR doll before selling it to Claude.
Stupidity: When Governor Swann is trying to encourage his daughter while she's locked within the ship's chambers trying to escape, she climbs down to a boat. Nobody in the Navy would have left a boat there, neither would Jack (and why would he, especially without anyone noticing?). The boat just mysteriously appears to help her escape.
Stupidity: A movie always needs extra conflict, but Julie's reasoning for walking out on Marcus and Mike is one of the dumbest. "If his wife can find us, I'm a LOT better off on my own." What sort of logic is that? She's the wife of his best friend. Of course she knows where he lives. (01:32:45)
Stupidity: When Alice opens the door for the dumbwaiter, how did she not see the bottom of the elevator was removed when she was looking right at it? She even realised it was missing as she was getting in, but she still let go and fell to the basement.