Stupidity: Whenever General Grievous fights another lightsaber-user, there's almost always a moment with all the sabers crossed dramatically in front of both participants, one preventing the other striking a killing blow. Looks good, but utterly ridiculous, because he's got 4 arms and 4 lightsabers - he could easily block the blade in front of him with one or two arms, and simultaneously swipe at their head and legs, which no-one with two arms could ever defend against. Of course that would make for a lot of very short duels.
The Return of Hydro-Man: Part 1 - S5-E7
Stupidity: When Spider-Man is working in the lab, he uses his webbing to barricade the door shut so no-one interrupts him. When Debra Whitman shows up and asks who is in there, he identifies himself as Peter Parker. When he is finished with his work, he leaves out of the window so that by the time the security guards break the door down, he has vanished. Since he used his webbing to keep the door closed, it would be pretty easy for Debra and the security guards to figure out that Peter is Spider-Man since Spider-Man's webbing is at the scene and Peter seemingly vanished into thin air.
Stupidity: Sir Topham Hatt is cross with both Percy and James. But why is James being blamed? He had no idea that Sir Topham Hatt didn't actually say that he had to stay in the shed and wait for him. James shouldn't have been blamed since he had thought Sir Topham Hatt actually said that and Percy should've been the only one blamed.
Stupidity: After eventually arriving at the stadium, why didn't Ash tell anyone that he was late due to getting kidnapped by Team Rocket? He arrived with half of his Pokémon exhausted and subsequently lost his battle. If he informed everyone about his situation, his battle with Ritchie would likely have been postponed until tomorrow, giving him some much-needed time to rest, which would have given him a bigger chance to win.
Behold, a Distant Star - S2-E10
Stupidity: When Johnny finds out his father is alive and wanted for murder, he is livid with his sister for telling him neither fact. When Sue decides to tell him the whole story, she asks Reed to pull a photo album from the drawer next to him, which contains a newspaper clipping detailing that their father was wanted for murder. If Sue didn't want Johnny to know about that, she shouldn't have placed the clipping in a photo album, and then kept the photo album in a communal area where Johnny could have easily discovered it at any time. (00:06:19 - 00:07:34)
The Succubus (a.k.a. Chef's Mama) - S3-E3
Stupidity: When Kenny and Cartman are sitting on the bench, Cartman can't start the tape as he has fallen asleep. Kenny then tries to wake him up, but wouldn't it have made far more sense for him to just start it himself, as he is sitting right next to it? Cartman's job was to push the play button. It was not like he had to rewind, fast forward or even eject the tape, so all Kenny had to do was just simply push the play button and tape would have started to play.
Stupidity: One of Rogue's defining character traits is her inability to have physical contact with another person because of her powers and the sorrow it causes her. Several episodes of this show, however, featured devices that could suppress mutant powers, the inhibitor collars being the most prominent. Despite this technology at their disposal, they never even think to have Rogue wear an inhibitor device for times she would like to touch someone. Even if she didn't want to wear those specific collars, a character like Beast or Forge could easily create a new and harmless device by reverse engineering and adapting the existing ones. This of course would eliminate Rogue's ongoing dilemma and potentially curb her development as a character, but it doesn't make sense from the standpoint that she longs for physical contact with others.
Stupidity: When the new principal is addressing the student body, Avalanche tries to impress Kitty by causing a couple of small earthquakes, one of which causes the scoreboard to crash to the floor below. The principal laughs off the incident and continues to address everyone instead of either evacuating the area or having everyone take cover.
The Secret of the Unicorn: Part 2 - S1-E4
Stupidity: When the Bird brothers are searching the treasure room for Tintin, one of them claims they have found him, and points. The other brother then shoots at him which was turns out to have just been a mirror reflection. The brothers then proceed to find Tintin and start by going straight forward, completely in a different direction than the mirror. If they wanted to find Tintin, wouldn't the more logical thing to do be simply look in the direction the mirror was pointing at? The whole point of a mirror is to reflect what is in front of it, so Tintin would probably have been standing in that direction anyway. (00:37:25)
Turkey Guys - S13-E5
Stupidity: The whole episode revolves on the turkey that Peter ate. Lois sends him and Brian out to get another one. She stalls dinner the whole episode waiting for them to get back. Problem is the turkey is frozen! It will take at least 6 or 7 hours to cook and Lois acts like as soon as they return with it, it won't take long to to cook, so the stalling makes no sense. (00:12:45)
What If... The Watcher Broke His Oath? - S1-E9
Stupidity: Ultron says he can destroy galaxies with a thought. So regardless of Dr. Strange's protection spells, he could destroy the planet they're all standing on, or evaporate the atmosphere, leaving them all suffocating in space, and just step away from the fight entirely while they die.
The Prison Prep School Murder Case File 5 - S1-E14
Stupidity: When the Puppeteer is shot, like any good villain he's actually wearing a bulletproof vest. However, a bulletproof vest is not a magical forcefield that neutralizes kinetic energy; this guy barely flinches when hit. Neither are flames; his fire trick raises a literal firewall, but firewalls are not literal walls, they do not stop bullets. The policemen could easily keep shooting through it (he throws a glove at Kindaichi through it), but they just do not, for no reason.
Win Mr. Stein's Duel: Part 1 - S3-E9
Stupidity: Adrian has a conversation with the other main characters whilst he is lying in bed, before they leave. Once they leave, he is revealed to have been wearing gear, which he hid from the other characters by covering his whole body with his duvet. There was no real reason he had to do this; he could've just worn normal clothes during the conversation and changed into his gear after they left. (00:05:39)
The Ringer - S1-E1
Stupidity: As Link is watching Zelda from his tower, he's completely distracted and oblivious to the Moblins entering his room from the floor. They have the element of surprise and one sneaks up behind him. But rather than doing the smart thing and say, stabbing Link in the back or delivering a crushing blow from behind while Link is unaware of his presence, the Moblin simply just grabs him on the shoulder and puts his arms behind his back to hold him while the other Moblins go for the Triforce. Giving Link plenty of ability to kick one in the face, free himself and grab his weapon to fight them off. The Moblin should have just gone for the stealth kill, even if they aren't all that bright of an opponent. (00:02:10)
Ayaushi shiryu! Cloth no hakaba - S1-E10
Stupidity: Saori blushes when Seiya opens the door shirtless...but she's seen him shirtless practically all her life, the boys kept training and fighting all the time. He even fought shirtless for the last part of his duel with Shyriu just the day before.
Iron Man to the Second Power: Part 2 - S1-E10
Stupidity: When the other heroes are watching Iron Man battle his robot duplicate, Julia cheers him on and calls him Tony. This fight is taking place in full view of the public, and the public doesn't know that Tony Stark is Iron Man. They believe that Iron Man is Tony Stark's bodyguard. Julia could have easily revealed Iron Man's secret identity in this moment. (00:17:50)
Young Kidaichi's Murder: File 1 - S2-E1
Stupidity: Kindaichi behaves in a criminally illogical way in this fourth parter episode. The original victim told 4 separate people some sort of keyword for the party, each one linking to another person. Kindaichi after at least the second if not the first victim could and should have asked EVERYONE (he had every opportunity for that) if they received such a 'password' by Tachibana before he died. Instead, he pointlessly follows the trail of breadcrumbs and two if not three people die for nothing.
Stupidity: There's no way April would mistake Slash, his debut episode in Season 4, for one of the turtles as he's got spikes on his back, dressed differently too.
Until Sunset, the Full Moon - S1-E7
Stupidity: This is not quite 'stupidity' but rather a "movie logic", supposedly sharp deduction that is really just a wild and nonsensical guess. Zenigata knows for a fact that Fujiko is impersonating Elena because she knew right away where to get the first aid kit, while Elena hasn't been in the mountain house since her husband's death. That makes no sense; Zenigata has to assume that Elena was completely straight about that fact (if it was the treasure's hiding place as he suspected, she easily could lie), and a person can easily remember where they store their security items even after years, for a variety of reasons.