Stupidity: While discussing his arrest with Emily, Seth mentions that he didn't tell the arresting officer that he works for Kirkman. As the White House's liaison to the media, Seth has a high degree of visibility; it would extremely difficult, if not downright impossible, to keep his place of employment concealed from the police for very long in the time between his booking and arraignment and when Kendra bails him out the following day.
Backlash of the Hunter - S1-E1
Stupidity: Rockford knows almost nothing about the guy who is tailing him except that he noticed him while he was grabbing a bite with his client. Regardless of that, he sends the same client to seduce him, just assuming that he won't be able to recognize her. And it works. Is Lindsay Wagner this hard to forget, that this guy just an hour or two later isn't able to tell it's the same woman his target was meeting?
Stupidity: After the accident, Dawn is in spirit form on the road trying to wave down an oncoming car (driven by Martha Kent). Dawn doesn't know she's a spirit that can pass through objects at that point. Since Martha can't see her, she keeps driving straight towards Dawn. Dawn sees the vehicle isn't slowing down and instead of simply stepping out of the way to avoid getting hit, she turns her back, revealing to the audience that objects can pass through her now.
Stupidity: Adam, Jason's replacement on Bravo team is operating as Bravo 1. He's in the midst of reloading his carbine rifle with a fresh magazine when he sees a suicide bomber running towards his team so instead of drawing his pistol which takes 0.7-0.8 seconds; he's a trained professional so that timing is reasonable; he instead charges the suicide bomber and dies in the explosion. It would've taken less time to shoot the threat than to charge him. (00:07:00 - 00:08:00)
Day 4: 12:00 A.M.-1:00 A.M. - S4-E18
Stupidity: After leaving the power plant to pursue the terrorists and retrieve the nuclear football, Jack orders the helicopter to take out the first Jeep. After he realises parts of the football are missing, why does he not order the helicopter to pursue and take out the other Jeep, preventing any further trouble from Marwan? (End of season 4's story, most likely).
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.
Stupidity: S50: Starting in episode 120 Genoa City had a celebratory gala at the GCAC. After the gala everyone that was staying long-term at the Grand Phoenix Hotel is now staying at the GCAC. The GCAC long-term rates must be much better to make everyone move out of the Grand Phoenix.
Stupidity: The emigrants lack guns yet after several bandit raids the team does not take the guns and ammo from the bandits to protect themselves from future raids. It's not like they can swing by the local Cabelas and stock up on guns and ammo.
Episode #1.2 - S1-E2
Stupidity: The part when the Colonel and the governess pose as journalists does not make sense. It's far-fetched enough that after a lengthy interview about the culprit's fortune the topic of his family never came up, considering it was one of the main goals and an ideal question to lead with, but considering that "mr. Todo" does not want a picture taken and has a tight security, there's no way that a photographer carrying a large 1930 camera would have been allowed into the interview room to begin with.
The Power of the Doctor - S13-E9
Stupidity: After the crew of the space train have taken out the Cybermen, the Cybermen begin regenerating, which one of the crew points out. This guy seems to be aware of how regeneration works, but doesn't shoot at them again. In the series, it has been shown that shooting someone during a regeneration cycle will kill them instantly, but this idea is never considered.
Stupidity: When they are conferring before surgery everyone is keeping scrub except for Avery who has his arms crossed. Shortly afterwards you can see him look around at all his co-stars, realise he screwed up and try to casually raise his arms. (00:15:00)
Stupidity: Mouch is investigating an arson allegation. He states to a lady he's going to do his thing and speak to some of the residents. As he goes down the hall to speak with the residents he passes a huge stain on the carpet that looks like blood or something and walks right past it without stopping. (00:23:57)
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.
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.
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: 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)