Stupidity: Ultimately, it did wind up working. However when they shoved the antidote vial into Claire's purse and got George's attention so he would eat her, this was an insanely stupid move. 1. They had no way of knowing if he would actually choose to eat her if he even grabbed her in the first place. Before then he'd been crushing people and even threw the helicopter pilot miles off the building while they watched that happen. 2. The antidote was in a plastic polymer like tube designed to hold the substance inside it while submerged in liquid nitrogen containment. Even if the gorilla's stomach acid could eat through the vial to get to the antidote, it would take hours for it to get through a material like that. 3. Gorillas are herbivores, so it wouldn't have tried to eat a person in the first place. (01:17:55)
Stupidity: Nobody is ever going to take a nine-year-old child on a dangerous mission to locate and destroy a marauding, giant shark, a project that has already cost a number of lives.
Stupidity: After the team break Solomon Lane out of custody, they drive around Paris with him in the front seat of their car. Lane is still wearing a straightjacket, bound in chains and has a black bag over his head. The IMF team drive him through crowded streets, past multiple police cars in full view of everyone just minutes after an armoured convoy transporting a dangerous prisoner (who everyone is now looking for) has been attacked. None of the Parisian police seem to notice this and none of the IMF team questions the tactical soundness of this approach.
Suggested correction: What's stupid about this approach? The IMF team is trusting that with their skills and experience they can easily evade any police that spot them. Which of course they do. Placing Lane in the trunk would have kept him out of sight but that doesn't really matter because they weren't planning on sneaking him out, they were planning on a quick escape.
Stupidity: When Han tells Drydon Vos that he and Tobias will steal unrefined coaxium from the mines on Kessel, Vos initially says no, as Crimson Dawn's relationship with the Empire would be at risk. Han then explains that the Empire wouldn't know they were working for Crimson Dawn. Vos then agrees but insists his top lieutenant Qi'ra accompany them, even though she is a known associate of Crimson Dawn and literally has their symbol branded on her wrist.
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: They could've used the flying chopper thingy to kill off the armed guys when rescuing the kids off the train carriages. That way they could have made sure they got every single kid rather than rushing to just take the one containing Minho (which they messed up).
Stupidity: The coast cities should have an alarm that detects the Kaijuns. If they do, they should work when the beasts are few miles away from the shore in order to give the people time to get to the shelters. Instead of that there are still people on the streets in Japan and on the docks in Los Angeles (in the flashback) while the kaijuns arrive from the sea.
Stupidity: Outside the bank, Mike and the first merc are having a shoot out across the parking lot. There is lots of room between them and around them. Yet a random construction worker, with a clear view of this shoot out happening, suddenly decides to take off running into the line of fire between the cops and the robbers and gets shot in the leg. Their was no reason for him to suddenly decide to run between them shooting at each other into the line of fire. (00:44:35)
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: After Roy escaped from the factory, he encountered a metal garage-door-type gate that was open at the bottom to the height of his knees. Trying to sneak away and in obvious pain from his injuries, it would have been quicker, quieter, and probably less painful if he crawled through the opening. Instead, Roy pulled downward on the chains, making a lot of noise, and it didn't even get the gate halfway up before he bent over to get out. The gate went up more after he stopped pulling on the chain. (01:15:29)
Stupidity: The metro police officer (and co-conspirator) went to the old cement factory where the other bank robbers were. Since the police officer (accomplice) wanted the money and did not want other police officers to be nearby, he called 911 and made an anonymous false report stating he spotted the person police were looking for and misdirected them further away. Maybe a good idea, but he made this call using his own cell phone. (01:12:20)
Stupidity: When they raid the warehouse as the criminals are trying to leave town, they load the girls into.a white van. A man (Bruce Willis) wearing a ski mask gets out of the passenger side and covers with his pistol as they load the girls into the van. The entire time the slide on his weapon is back, so the gun is not ready to fire.
Stupidity: The building is supposed to be without power - at all since the generator has been destroyed - and life support machines are not powered up, but the 3D printers in every room are powered up - so that the good guy can squish the bad guy's head in it, and the elevators, so that the good guys can escape. What sort of hospital has its electric grid rigged in a way that the elevators keep working but critical surgical equipment goes dead the moment the power fails? (01:12:00)
Stupidity: At the end of the movie during the shootout. Cops would not engage in automatic gun fire with dozens of civilians in direct cross fire. Why not get a chopper and chase them down a bit maybe in an open area with fewer civilians? Then maybe engage in gunfire.
Stupidity: While running "silently", the SONAR keeps beeping. Active SONAR is akin to yelling "Polo" in a pool.
Stupidity: The team raids the house and locates 5 people inside deemed to be Russian operatives. They are subdued and placed on their knees, while some of the team works on gathering intel from the home. The subjects should have been handcuffed/zip-tied. Since they were not they were able to grab stashed weapons and cause a gun fight which led to one of the entry team's members being killed and all the Russian operatives killed. It's common knowledge to restrain people. Cops and military always restrain. (00:04:00 - 00:12:00)