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: 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: 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: 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: For someone trained like "H", it was absurd that he would run down the center of the road toward masked gunmen and get shot multiple times. It was also ridiculous for him to have taken his son to a location that was potentially dangerous and put him in harm's way in the first place. (01:13:20)
Suggested correction: I'm not sure how much H was trained. If I recall correctly he's a skilled criminal, and all his "training" was faked so he could get the job with the company. Regardless... training or not, all that goes out the window when your child is being attacked. Paternal instinct took over and he was rushing in to protect his son. As for your 2nd point, it's made clear that his task was to simply stake out what was supposed to be a routine truck route. They had no idea the truck was going to be robbed.
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: Why would the tow driver go around Deacon's truck in the one-way dead-end parking lot to pick it up from the front? He'd have to back it up on the hook, and Deacon's truck would be in Park, making it impossible. There's a reason tow trucks hook up vehicles by the drive axle ends. (00:08:40)
Stupidity: During the lightning storm, Hannah and Connor did not stop running through the open field when they reached the low point (dip). Hannah kept telling Connor to run, stop, and crouch even when they were headed uphill. It would have been safer to crouch at the lowest point in the field. Connor fell a couple times and Hannah also fell (or got struck) - both ending up doing one of the worst things - lying down on the ground instead of minimizing contact. (00:53:39)
Stupidity: The location of the small hole near the bottom of the wood-trimmed wall where Everette passed Sharyn a note and pencil would have taken much more time and effort to accomplish compared to merely penetrating the wall a little higher (where there would not have been wood trimming/baseboard on both sides). (00:10:00)
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: Instead of breaking into Gordo's house, covering all the furniture in one room with sheets/thin blankets, and waiting for Gordo to return home in order to kill him via a "dramatic re-enactment" (in an adjacent room which was not shown to the audience), Bill could have taken Gordo anywhere to avoid getting caught or calling the police on himself. Had Bill taken Gordo to his already-"wrapped" motel room, he had enough injuries after the fight to claim self-defense against an intruder. (01:43:20)
Stupidity: To quietly kill the hotel valet he is replacing, Diabolik throws a knife at him from distance, hits him in the back, and then drags his body in the middle of the street to the nearest manhole, leaving a long streak of blood he does not conceal. If this sounds pretty risky and unsafe especially for a meticulously planned murder, you have also to consider that in the comic book from 1963 this movie otherwise faithfully adapts, Diabolik did nothing this foolish; he quietly killed the guy strangling him next to the spot he'd dump his body into.
Stupidity: David and his partner Cal drive into a weeded area near the garage/warehouse the drug bust is going to be made. David says, "This might go south. We need backup." David and Cal sit in the car talking about not letting the product get onto the street where someone might die, etc. then exit the vehicle without calling for backup, which could have been done in a few seconds (and should have been done as soon as David said they needed backup). (00:02:10 - 00:02:37)
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)
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)