Stupidity: Ashley Judd finally tracks her husband down and what does she do? She doesn't try to capture him to prove her innocence, she doesn't notify the police, she doesn't take his picture and send it to every police dept in the US, she doesn't even follow him to find out where her son is. Instead all she does is ask for her kid back. What was she going to do even if she got him back? She is still on the run from the law, with little money and resources and she doesn't even know if her kid even remembers her.
Stupidity: When Cathy, Chris and Carrie go into their late grandfather's room, they discover a copy of the grandfather's will that states that if it was ever discovered that Corrine had children, she would lose everything. Had they taken the will to their mom's wedding and showed it to her fiance, they would have been able to expose the scam much quicker. Instead, they take the dead mouse Fred with them and show it to everybody. What good would a dead mouse do when a will has more leverage?
Stupidity: After Josh runs away from home after being turned into an adult, nothing seems to be done about his "disappearance." The only indication that he is missing is his picture on the back of a milk carton. There's no flyers about him missing. No mention of his disappearance in any newspapers or TV news about his mom saying that he's been "abducted" by a stranger. Even when Josh writes a letter home, he uses the actual address of where he's staying, but no cops turn up at his door after his mom receives the letter.
Stupidity: If the song "Beyond the Sea" can be continuously broadcast on the radio station as a "cryptic clue" that there are survivors living on the island and the aliens are unable to swim, then someone could verbally announce that information over the radio and otherwise communicate with other humans. The same thing about how Regan's hearing aid incapacitates the creatures. Rather than explaining how to weaponized the high-frequency sound, only the hearing aid's noise is broadcast and anyone hearing it has to figure it out.
Stupidity: Someone with the Punisher's tactical knowledge would not hang upside down from a chandelier to shoot in a 360-degree pattern at his targets. This would make him a sitting duck and it's only because of the movie tropes of Stormtrooper aim and cannon fodder henchmen that he isn't killed because of it.
Stupidity: Mrs. Doubtfire used the bathroom without first locking the door, enabling Chris (or anyone else) to walk in on her. A man who is dressed as a woman and doesn't want anyone to find out would make sure the bathroom door was closed and LOCKED. (01:07:09)
Stupidity: At the end of the film, the Rehabs recruit gang members and give them all kinds of guns from shotguns, handguns, and automatic weapons. The cops and deputized citizens have similar weapons. But for all the shooting, not one gang member is hit and only one citizen appears to be shot (aside from the three blown off the building roof by the Rehab tank.) I don't think anyone has any bullets.
Stupidity: If Jordan was inside the cake and the cake was right there in the room when the takeover began how did the bad guys forget she was still inside?
Stupidity: Bori Khan is a skilled archer and a man without honor. He's not fighting fair, and cares just to win, as established and explicitly said. He shoots an arrow at Mulan, the Witch gets in the arrow's way sacrificing herself to protect her...and for no reason whatsoever he does not shoot anymore, giving the chance for the two girls to share their very special dramatic moment together, but creating a colossal plot contrivance. It is a know movie cliche for the fight to 'pause' around the main character, but here we have a sniper who desists completely (he won't shoot anymore) for absolutely no reason. (01:29:00)
Stupidity: You'd think that Jezzie would have been a little smarter as a secret service agent. You know, like once they acquire Megan, to delete all the incriminating evidence sitting back on an unattended computer. Aside from the fact she also used quite a stupid password, a single password isn't very secure at all. And then the content, displayed instantly when you get in, might as well say things like "hey look, we know what the kidnapper looks like" and "wow, here's the boat he's in too" and "wow, a cabin for sale. Why don't we go hang out there with all the evidence." Come on....they might as well have left a trail of breadcrumbs, because they sure were asking to get caught.
Stupidity: During one of the test drives, the hook that Hiccup uses to fasten himself to Toothless gets bent, so he takes Toothless to the blacksmith to cut the line. There are two ways he could have easily avoided this: He could just unhook the saddle, take that to the blacksmith and cut himself loose, or he could just untie the leather strap. What he does here is needlessly risky and just there for his awkward conversation with Astrid.
Stupidity: Monk steals the magazine from Coffey's SIG. However, I don't see how he could have jacked the slide to eject the round in the chamber without being noticed. Someone as paranoid as Coffey was at this point would not have left the chamber empty. (Just FYI, when you load an automatic pistol with a magazine, you have to pull back and release the slide to load the first bullet in the barrel.)
Stupidity: When Greg volunteers to watch the security monitors to see if the creatures can affect people through a screen, no-one even thinks to remain in the room with him to cover up the monitors with a blanket, towel or something similar in case the creatures' power can be transmitted that way. They tied him to a chair to reduce his chances of committing suicide, so they certainly thought there was a possibility that he would be in danger.
Stupidity: Major Franklin is struggling up the side of the cliff while the rest of the group are on top of the cliff checking their equipment, then he slips and slides down the cliff side, breaking his leg. After seeing this, the group members reach for a long length of rope that was used to bring up the other members and the supplies. The commandos could have used the rope to help Major Franklin climb up and prevent him from falling and injuring himself.
Stupidity: Why does the team choose to enter the shimmer from Area X and then trek for miles to the lighthouse? They could travel by sea and stage an amphibious landing on the shore right at the foot of the lighthouse. Obviously this would make for a very short movie, but this choice still needs to be explained in the plot.
Stupidity: When the army base gets overrun the girl jumps on a soldier and starts biting his neck. The woman soldier that's with him aims her gun at them but doesn't shoot, knowing full well there's no hope for the man. There is utter carnage going on all around them and instead she tries to help him and gets attacked in the same way. This could be a plot hole as well as the girl in question is the one that holds the key to survival.