Stupidity: Captain Poison has a fairly good idea of where Solomon buried the diamond. We know this since when he leads the captured Solomon to the spot, there are already several holes dug looking for it. Despite knowing roughly where the diamond is - down to a relatively small area - he makes no serious effort to excavate the ground, instead contenting himself with a handful of incredibly shallow holes.
Stupidity: At the outdoor market, Libby told her old girlfriends that she'd "be right back" and went into a stall in the women's room. Soon, her girlfriends came in but stayed in front by the mirror. Without bothering to look if anyone (particularly, Libby) was in one of the three stalls, they started talking negatively about Libby (e.g, " Ugh, what is it about her that is so irritating?", "I feel sorry for her", "She looks like she's wearing a Halloween costume", "She's like a lumberjack"). (00:55:08 - 00:56:00)
Stupidity: While Mr. Butler was upstairs taking a shower, Lucas goes into his house, kills his wife, and takes the baby to the school (into Mr. Butler's classroom). Lucas wanted to take away Mr. Butler's family, so all he needed to do was also kill the baby at the house (or leave the dead baby outside on the porch for Mr. Butler to panic while searching). Lucas could have left the house without getting caught for committing a double murder; instead, he keeps the baby alive and assumes Mr. Butler will know he took the baby to his classroom. (01:17:53)
Stupidity: When they are preparing for a German assault towards the end of the movie, Miller explains to them the concept of the sticky bomb and adds, "If you have a better idea of knocking the treads off a tank I'd like to hear it." Um... The bazooka? They had eight rounds for it, and it could have easily been used to disable the treads. And the men wouldn't blow themselves up with it. While it couldn't destroy a tank by penetrating the armour, it's certainly strong enough to disable the tracks.
Suggested correction: Allied forces familiar with the Panzer VI "Tiger", a 60-ton Main Battle Tank during the war knew that the armor is very tough and, even with support fire from a friendly tank, the odds of destroying a Tiger tank with a bazooka like Horvath's are pretty small. From the infantry perspective, techniques that were developed and employed in order to combat heavy Tiger tanks focused mainly on disabling the tank rather than destroying it. Anti-tank weapons of the era, such as the bazooka, were ineffective against most areas of the Tiger's armor, so specific weak points in the design were the focus. Hitting the Tiger in the tracks, suspension, engine compartment, observation slits, and in the joint between the main body and turret were some of the common weak points. Tiger tanks could only be destroyed head-on or from the sides by land mines, or direct hits by heavy artillery shells, or bombs dropped from aircraft. In the film, the first Tiger is disabled by taking out the tracks with "sticky bombs" followed by grenades thrown in the turret hatch. When Horvath fires at the second Tiger, both shots are placed on the joint between the body and the turret, the idea most likely being to hinder or incapacitate the turret's ability to swivel left or right. As the war went on, the Allies developed better strategies for disabling Tigers. One example involved British Cromwell or US Sherman tanks trying to "flank" a Tiger by working in squadrons or columns. One or more tanks would act as a diversion to keep the Tiger's crew focused in front of it while another tank would maneuver behind the Tiger and hit it in the rear section where its armor was the weakest.
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: 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: All the mutants on the island need Magneto at the last second to take control of the missiles so they don't land and explode. Why didn't Azazel just teleport everyone off the island?
Suggested correction: Given the situation, there was probably very little time to come up with a plan like this. The missiles were flying towards them extremely quickly, and there would have been nowhere near enough time to band every single person together for Azazel to teleport them all out of there in just a few seconds.
There was plenty of time. He could have taken 5 at a time down the Beach 3 miles and came back for the rest. Earlier in the movie he was moving so fast men were falling from the sky at nearly the same time and he was teleporting them one at a time.
Stupidity: The fact that Nolte even gives in to Eddie's demands is ridiculous. Why not just interview him in prison, ask him where to look for certain people, etc, and if it's a dead end, report back and ask for further tips, etc. They had zero problem going to prison and asking Kirkland Smith in the sequel.
Suggested correction: He refused to tell him anything unless Kates takes him out of prison.
Stupidity: The marble somehow got under Don's skin at the bottom of his leg and was moving up the length of his body. Instead of heading off the marble in order to intercept and stop it from continuing up his leg, Don got a knife/box cutter and jabbed it into his skin near the bottom of his leg and trailed the marble, causing a long gash that served no purpose (other than creating a lot of blood and making a gory scene). The marble eventually exited his body via his eye. (01:04:40)
Stupidity: It was very idiotic of Turner, who is an experienced serial killer, to not only knock out and take Julie prisoner, but to attack Kale as well, considering the recent circumstances. The police and Julie didn't believe Kale, and Turner suddenly goes on a rampage? He took a huge risk when he attacked Kale and could have very easily blown his cover.
Stupidity: In the opening scene, Sonny has come to her now-deceased father's house. Police and the coroner are in the basement taking notes while standing around the body - which is face down and awkwardly lying at the bottom of the steps. Det. Sabatino informed Sonny that the death was ruled accidental due to a high blood-alcohol level. Detectives or the coroner did not rule out other possibilities: natural cause, suicide, or murder. High blood-alcohol level could be secondary.
Stupidity: When Poirot's team attacks the Germans, they do it through the cover of gas they release. The Germans are having a good time chatting and not taking the situation seriously when there's a big cloud of noxious gas advancing towards them. Despite Poirot's oh-so-clever plan, they should by all means know that something is coming their way, but they get caught entirely with their pants down.
Stupidity: With the threat of strangulating Jess, Garriga coerces a false confession from Nicky about the complicity of Jess. Garriga then laughs, calls Nicky out on it, and points out the confession's deficiencies. The film treats the whole scene as an astute reveal à la Sherlock Holmes! Nobody notices, let alone points out, that a coerced confession is worthless. In reality, Garriga would feel very stupid because he almost murdered someone. For the same reason, Jess must feel very angry.
Stupidity: At the very beginning of the movie, law enforcement is depicted executing a no-knock warrant. They approach a house surreptitiously and use a ram to open the door with no warning. When they arrived at the scene, all the cars and trucks in the raid were using flashing lights and wailing sirens. So much for the element of surprise.
Stupidity: Lyla does not like the idea of Mickey fighting and initially does not want him to agree to the fight. Lyla eventually tells him "okay", but he must stop when she tells him to stop. This may give her a reason to go to Dubai, UAE with him, but she is about 8 months pregnant. An international flight has some risks plus she would be far away from her OB-GYN doctor if there were a complication. She should have had enough sense to avoid international flights/traveling so close to her due date.
Stupidity: Becky possessed the mysterious key that the four neo-Nazi prison escapees were at the lake house to retrieve. Becky didn't know what the key was for, so did not have a vested interest in it. By first denying that she knew where the key was and later refusing to give it to Dominick, her father was killed. Had Becky simply handed over the key when Dominick asked for it, it is possible no-one would have been hurt/ killed. Becky keeping the key with no importance to her served to further the plot.
Stupidity: The end fell apart. It took convincing to get the police at the picnic area; however, while Jack was cracking up, they just left alone with his gun. After the stakeout was a bust, why didn't the police just question the girl: "Who told you to come here? Who was to meet you here?" Also, they police see a smashed black station-wagon. Was there no connection to the previous child's drawing?
Stupidity: Colette was holding the metal ladle close to the bottom of its long handle and near the top of the hot pot of stew she was serving, and yelled, "Ah." due to her hand getting too hot. She had a towel wrapped around the handle of the pot, but it was that hand that got too hot/burned (not the hand that was holding the metal ladle close to the top of the steaming hot pot of stew). (00:04:48)