Stupidity: Shriek is being taken to a new facility for superbeings, after a medical exam established that her sonic powers that she has been using since she was a kid are too strong to keep her at the correction house. So "naturally" for this transport she is not gagged, sedated, not even bound, and there's just one guy with her, not even wearing earplugs. It couldn't possibly be any more comically unsafe.
Stupidity: A major effort is put in the future to develop the time portal, so they can recruit people from the past to help fight the war in the future. Yet they never seem to think to share anything with the past about the creatures and how to kill them or find out where they came from so the can help either prevent it from happening or help save the future before humanity is wiped out. Muri does recruit Dan for this purpose but it seems wasted to only use 1 person for this much more important goal.
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: 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: When the rebel leader talks to Rick Flag guaranteeing her help, she mentions that she will help to find "this Gaius Grieves", speaking as if it was someone unknown to her. He's been around the island (going to bars and surely not being reclusive) for 30 years; it's pretty difficult to think it would not be one of the most known people on the island, given his role, unique appearance and the small community.
Stupidity: After the fight in the woods Bond walks back a long way, instead of driving the Toyota he had left in the forest in full working order.
Suggested correction: The Toyota has had a major chase over very rough terrain, it may no longer be operable.
It was operating fine when they stopped it in the middle of the forest.
Stupidity: Arishem's plan with the Deviants hardly makes any sense; he sent out biological beasts that he can't control, to kill off the natural predators of every planet. Forgetting the fact that obviously it didn't work (but the movie does not say that) because Earth has always had predators, that's a terrible plan to begin with, since any ecosystem needs predators or the other animals will grow uncontrollably.
Stupidity: Liv and her five friends went to Willy's to set it on fire, but Liv insisted they first go inside to get the Janitor out. All were aware of the situation and danger related to the mass murderer and the animatronics, but Bobby and Kathy went into another room to "hook up." Kathy recognized the room as the one where the killers committed suicide and later saw movement, but she continued having sex with Bobby until he was attacked and killed. (00:38:48 - 00:42:02)
Stupidity: To save the people from rubble falling on their heads Flash does not move them aside like he did with his future love, but does some strange manoeuvre which takes seconds - since we see people moving normally - and happens in midair (how does he get there?) and that does not take care of a huge chunk of concrete which he does nothing about, shouting just "No!", but Cyborg has all the time he needs to load his Mega Man arm and vaporize it in midair. (02:00:00)
Stupidity: Natasha is in Norway on the run - Norwegian radio mentions her by name, Yelena talks about her being on magazines, she's very recognisable, and yet she goes into a gas station with her sister without changing her appearance in any way, and loudly talks about being an Avenger and killing people, right in front of the gas station attendant who for all she knows would be on the phone to the authorities the second she's out the door.
Stupidity: When the crew think that Dorothy is a robot with a bomb planted in her and is capable of exploding, they begin to think that she is about to explode and attempt to dodge it. Rather than hide somewhere or take cover behind an area that may protect them, they just get down on the floor in front of them and cover their heads with their hands. If they thought the explosion was going to be as deadly as the one they saw on the news, this method of taking cover wouldn't be even remotely effective. (00:24:40)
Stupidity: For claiming to know how to deal with Music Ebo doesn't do a good job. He wrestles her to the ground to calm her down which is very dangerous for both the patient and the caregiver. It's only recommended as a very last resort and in both scenes with this neither one required it to be used.
Stupidity: Dahlia, fleeing her husband, asks Parker, "Well, where we [her and daughter Ashley] gonna go?" Parker replies, "I know a place where you can go" and takes them to Marcus' house, parking his car there. (Mikey and Louis are looking for his car and find it.) Parker, though recently fired, is/was a social worker. Social workers are among the professions that have the greatest awareness of available community resources. Parker should have taken them to a shelter or other safe place. (01:06:04)
Stupidity: Peter and Amanda were wealthy enough to buy the 11th floor penthouse for $579,000 but had no security cameras. Also, Det. Martinez never thought to check surveillance cameras outside the Wright's penthouse; surely cameras were around and/or the Detective could have questioned neighbors if anyone saw Charles near the penthouses or with the Wright's dog Humphrey. Peter or the detective could have gone near Charles' boat without a warrant and called Humphrey to see if the dog barked in response.
Stupidity: While awaiting their flight home, Nancy told Teri, "Think I miscalculated the tea. I'm not gonna last three-and-a-half hours [on the non-stop flight with no restroom facility]." Nancy then went into the gift shop where Stuart Couch introduced himself, asked if he could get her a drink, and bought her a bottle of beer. Nancy drank at least some of the beer on screen, even though she was already concerned about drinking tea before her flight. (00:59:28 - 01:00:30)
Stupidity: Patrick told Dwayne to get Cisneros to kill Zara, apparently because he believed Cisneros could get the job done. Cisneros went into Zara's house with his gun ready to shoot, but not before pinpointing Zara's location. He saw the refrigerator door open yet entered the room without looking left and right (behind the door); Zara was able to disarm him. Zara was also able to escape Cisneros' repeated crazy swings at her with a samurai sword. Zara fatally "sliced" his neck with a pizza cutter. (00:21:44 - 00:23:07)
Stupidity: Luca's parents try to find him by splashing him with water. If they succeeded, Luca's cover would have been blown.
Stupidity: Ben is standing behind Marley with a gun to her head as protection against Aaron, who is pointing a gun at him. Aaron shoots Marley and Ben just stands there, first looking at Marley on the ground then looking at Aaron (standing about ten feet away). Aaron screams and shoots Ben in the abdomen. After Ben falls, Aaron shoots three more rounds at him but misses. Ben is also able to stand and walk around despite his abdominal wound. (01:17:30 - 01:20:40)