Stupidity: In 300 years, in an empoverished world full of people hungry for techs, nobody ever tried to remove the ship from a small pond barely 15 feet deep, and everything inside seems intact. It is mentioned that few tried because the technology is hard to sell being unknown (which is laughable), but surely some would try to strip the ship for alloys, and certainly the lights and monitors wouldn't stay untouched in a world based on scavenging. For 300 years and so close to the city, even.
Stupidity: The train which takes M from New York to London arrives looking like an old tube train, then when she's on board converts into a high-tech train, to her amazement, and whisks her across the Atlantic. Except...why did it ever look like a regular train? She's in a MIB station, it's only used by agents and aliens, it goes to another MIB station, and when it arrives and people get off / on before it continues its journey, it stays in its high-tech form anyway.
Stupidity: When Roy finally gets to the Lima project in the shuttle but can't dock, he just lets it drift away - he could have at least tethered it to the station to use it for his return trip.
Suggested correction: There is no way to know the reason why he did this. It's plausible, or even likely, that the pod was out of fuel. Not only that, but it could not dock with Lima because it was damaged, so it's likely that the damage played into the decision as well.
Stupidity: In the opening scene with the military convoy, the two soldiers in the lead vehicle never notice the car veer into their lane, even though their faces are bathed in bright light from the car's headlights. They simply ignore it and keep talking to one another.
Stupidity: While Tommy and Snake Eyes are trying to escape the docks in the truck, the Yakuza men surround the truck and stab over a dozen swords in all parts of the cab. Not one of the men ever thinks to use their sword to slash the tires, allowing the heroes to make an easy escape.
Stupidity: When Wolverine is trying to prevent Deadpool from sacrificing himself by destroying the time ripper device, he repeatedly pounds his fists against the glass panel on the door to break it, to no avail, which leads him to then go to another heavy door, which he is only able to break down in the nick of time. Wolverine's adamantium claws would have easily destroyed the glass on the other door, without him having to repeatedly and futilely punch it.
Stupidity: Kord Headquarters goes into "lockdown" after the Scarab is stolen, which in this building, apparently means allowing all the guests to leave.
Stupidity: During the auction, we see the dinosaurs are brought into the room and placed in the middle. Thus blocking half of the bidders from the auctioneer's view. (01:16:40)
Stupidity: Colonel Sharpe retrieves a gun from a locker on the Freedom shuttle. However, said gun is shown lying flat on the floor of the compartment, with no visible means of securing it, which would hardly be standard NASA procedure given the shuttle undergoes a high-G launch, orbital manoeuvres and various other high acceleration events. A loaded gun bouncing around is the last thing anyone would allow on a shuttle. (01:42:39)
Stupidity: When the Pteradons are loose and flying over the crowds, people run from inside buildings out into the open where the birds are attacking people. (01:22:00)
Suggested correction: A person is smart, people are stupid. A crowd in a panic would do exactly that sort of thing. Like trampling over each other running in panic from a shooting or a fire when not needed. It's the nature of panic in humans as a group to act stupid. It's not a movie mistake. It's actually one of the more realistic parts of the film.
Suggested correction: The dinosaurs were also breaking into/attacking people inside, so they weren't safe no matter what.
True, but one option is certainly safer than the other.
Stupidity: Having become the leader of the universe's most stealthy fighters, he promptly leads them in a Custer-esque noisy frontal charge into a force with known weapon and technology superiority. Zero effort to utilize ANY of their amazing stealth, just have them slaughtered so badly that the planet has to sacrifice animals to save them from extinction.
Stupidity: We know that the two 'special visitors' have been in our universe longer than a day. Despite being capable, smart, heroic figures, they did diddly-squat until the plot says so, since they haven't tracked down the very public (they recognize them) partners of Spiderman, they don't show up for the battle broadcast by JJJ on giant screens, but more importantly, they do not know who the "Avengers" are, showing they didn't look into Peter's history - the name would have popped up in relation to Stark, the blip and much more. Seems that they didn't even try to look for him.
Stupidity: Everyone laughs off any reference to the supernatural and the Ghostbusters being any more than hacks. However, they drilled a hole that unveiled a literal river of pink glowing goo that is even brought up at the trial; nobody investigates its origin or acknowledges the fact, which is exceedingly absurd since it involves heavy pollution of the underground system of a metropolis.
Stupidity: In the freezer you can see the electrical wire power cord that is powering the motor on the wall. She could have easily pulled/ ripped the wire to stop the freezer from working. And when the chemical bomb is in the mixer they could have unplugged the machine which would stop it from going off.
Stupidity: Given his speed, surely Superman could've stopped both missiles with no problem.
Stupidity: There was no particular reason for Nuclear Man to take Lacy into the space in the first place.
Stupidity: Knowing that the Klowns' noses are their weak point from previously shooting them, Dave doesn't bother to shoot the giant Klown at the end with his pistol, instead waiting to be almost crushed and finally popping it with his badge pin.
Stupidity: Stitch wakes up in a kennel with dogs at the animal shelter. When Lilo picks him out and they walk out of the kennel, the lady freaks out and tells Nani, "We thought it was dead, it was hit by a truck!" So, what was thought to be a dead dog was put into a kennel with other living dogs. Think about that for a second. (00:24:54)