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: 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: 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: 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: 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: 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: The Analyst wishes to hide the true identity of Neo from anyone inside the Matrix, so his appearance is altered. But in this new Matrix Neo is also named Thomas Anderson, his name from before he was pulled from the Matrix originally, and he is a famous game developer that created a video game series called "The Matrix." It is frankly astounding that anyone actively looking for Thomas Anderson would not immediately see through this ruse and instead would be fooled by balding hair.
Stupidity: The "body armor" General Ford and others wear is very bulky and appears to be quite heavy with all the attachments (e.g, flashlights on shoulders). With the protective suit protruding perhaps 8", it would most likely restrict/slow movement, contrary to what soldiers need. Moreover, the body may be protected, but there's no protection for the face/head, leaving them exposed/vulnerable. Today's products tend to be lighter, thinner, and stronger, so would be expected in the future.
Stupidity: Right before the movie's final battle, Sub-Zero taunts Cole with his wife's necklace and makes him chase him into a portal. Sonya was right next to Cole, and she did not come along with him. They had previously planned to take on Sub-Zero together, but apparently she just left him to chase Sub-Zero alone to an unknown location.
Stupidity: Two things: 1. I find it inconceivable that there is only one Carbon Dioxide Removal Assembly (CDMA) and no spares for a two-year mission. 2. The crew has 20 days to fix an oxygen problem. The commander decides on a 10-day window. 5 days into that window they try to load oxygen from the Kingfisher spacecraft. One is lost into space. Zoe decides to go and fill the other one in the midst of a solar storm that will only last hours. Why take that chance? A few hours wait is still quite possible.