Stupidity: After Bernie discovers a treatment for the infection, radiotherapy, everything goes back to normal. Except the contagion is airborne (which is why they were going to flush the entire ship's atmosphere), so they're just going to re-infect themselves in a few hours. And there's only one room on the ship that can be exposed to stellar radiation, so there's no way to clean the atmosphere either.
The Pin-Up - S7-E17
Stupidity: After Erin leaves with the military captain to Camp Lee, John and Maryellen turn around to see John Curtiss nowhere around on the porch where Maryellen left him. So John goes off to look for him, while Maryellen goes in to check The House. John Curtiss is a one-year-old baby who couldn't open a door.
The Night of the Firebrand - S3-E2
Stupidity: West is introduced to, then knocked unconscious by Vixen as she hides a club behind her back. A trained Secret Service agent like West would not have let his guard down in this situation, as the entire fort was awash in bad guys.
Stupidity: The experienced cop Pullman enters the house of the well-known badass villain with her partner only, without any more backup. After the partner gets killed, Pullman stands free in the middle of the room without any cover - just 'begging' to get shot dead. (00:53:15)
Camp Redwood - S9-E1
Stupidity: Brooke leaves her apartment window open as she sleeps, even after telling her friends that serial killers (like The Night Stalker) strike during the summer when everybody leaves their windows open.
Stupidity: During a raid of a Latin stash house, Hailey and Kim find two girls with a pistol. In Spanish, they say no bullets. Kim interprets what the girls say and Hailey replies, l didn't know you spoke Spanish. Makes no sense that a partner on an elite police unit in Chicago would not know a member of the team speaks Spanish. (00:14:58)
Stupidity: Despite being a high-profile fugitive who was a local celebrity in his previous life, Saul does very little to alter his physical appearance, settling on just a mustache and glasses. Growing a beard, wearing a hairpiece, and altering his speaking voice around others would have gone a long way in preventing him from being made.
Who, What, Where, Wendigo? - S2-E10
Stupidity: Dwight, Audrey, and Nathan all know Dwight's trouble is that all bullets are attracted to him, so why is he with them when they go looking for the killer, knowing every one is using a gun?
Stupidity: An explanation is given for the reason why the bombs planted on the Gundam are not activated by remote control (they have plastic explosive in the regiment but not remote controls!), but no reason why they set the timer for the explosion to 30 minutes, way too much to be of any use in combat against the Gundam. Moreover, if the vulnerable spot of the Gundam shield were situated where it explodes at the beginning, it'd be completely useless.
Stupidity: Harold isn't sure whether to trust the flash drive Claire gives him, worrying connecting it to his laptop will send Samaritan all his personal connections. Somehow it doesn't occur to him to just use a completely disconnected / airgapped laptop, in a Faraday cage or similar like the one he kept Root in. If the flash drive had malicious code on it, nothing could be transmitted anyway.
Worlds Apart - S1-E2
Stupidity: The bad guy kills the deputy in the swamp, then later sees a little girl who witnesses the killing run away. He then searches the boat for a weapon and runs off after her after he finds a machete, without even considering the officer's gun still in its holster. Abby proceeds to make the exact same mistake later when she finds the dead officer (meaning there's danger nearby) and hears the girl screaming and runs in the direction of the screaming without taking the gun to protect herself.
The Perks of Not Being a Wallflower - S1-E3
Stupidity: Superman finally smashes the weirdly strong bad guy through a wall, then goes to Lois, says "he's gone", and whisks Sarah to hospital. But he has no idea if the bad guy is "gone" or not - they've just had an epic fight, he has some sort of super strength / resilience, and for all Superman knows he'll come around in 10 seconds and finish the job of murdering Lois.
Suggested correction: Superman knows the 'strong bad guy' is close to his own strength. After fighting him, he knows what effect the crash through the wall would have had on him, if he was knocked out, and how long he would be out for. So he knew there was little risk of the guy coming around in 10 seconds. Alternatively, he X-ray scanned the area and saw the guy was no longer there.
Stupidity: Ray, Avi and Lena covered up a murder. Ray tells Avi that Lena rented a car in The Dead guy's name, and he needs Avi to drive down south, use his passport at the border, and then to fly to Mexico City. The Dead guy's passport has been altered with a picture of Avi, however still in the name of The Dead guy, Varick. All border crossings and airports have security cameras. If they ever want to look into Varick's disappearance they can search his name and see it is not him at the border or airport. (00:42:23 - 00:43:00)
Stupidity: After Walks on Cloud releases Dr Mike, she runs off and hides in a wild thicket as the Dog Soldiers and One Eye look around the area for her. A pair of buckskin are then seen scoping the area, then walking off as Dr Mike leaves her hiding spot and gets 'surprised' by One Eye, who knocks her out. She should have known better and stayed put until sunrise, as Sully taught her when it came to the Cheyenne war parties.
Two Hundred Dollars and a Bus Pass - S1-E8
Stupidity: Two police officers and a physician find an injured woman in a lab. The officers attend to the woman while the physician calls for EMTs. Wouldn't it be better if the physician looked after the injured person while the officers called for help?
Stupidity: Dr. Greg seems to catch some of the more obvious quirks of inmates attempting to take a large vial or bottle from the cabinet. Yet he doesn't seem to notice when Lizzie grabs a bottle of pills and pockets them from the rolling cart in front of him. (00:20:15 - 00:20:45)
Stupidity: The inspector knows that his house has been bugged; he does not know how many bugs and cameras are there, he just knows there are some. He does find a bunch of them with great ease when he gets back home - making you wonder how could he have ignored them to begin with, since all it takes is for him to raise his eyes, they are fairly big black cameras who do not camouflage at all for the most part. He then proceeds to make a phone call to the big baddie from his landline. Nobody in their right mind would do such a thing. Heck, you wouldn't want to use your home phone for such a call even if you didn't know that someone just put bugs all over your house.
Stupidity: On 8/12/04, Hope specifically told everyone that when the coin was thrown into the force field, there would be a bright flash and that they shouldn't look at the forcefield when this was done. But all three times that the coin was thrown at the force field that day and the next, everyone looked right at it the whole time, and then recoiled in pain at the flash that inevitably occurred.