Girl Trouble / School Dance - S3-E18
Stupidity: Girl Trouble: Helga pulls a nasty prank on Arnold in class by gluing feathers to his bottom. Mr. Simmons sees this, but for whatever reason, does not give Helga detention for it. The next day, Helga spills paint on Arnold, then he throws some on her as revenge. Mr. Simmons sees this and gives Arnold detention even though he was simply fighting back at Helga for pushing him too far. Perhaps Mr. Simmons' brain was on vacation those two days. (00:03:16 - 00:08:42)
Stupidity: In the flashback, Emily's sister takes ill while playing her flute. In the next scene, the sister is sick in bed and Emily now has the morpher around her neck, but she is in the exact same outfit. If the sister was forced to pass the legacy on due to disease, it should have taken more than just a few minutes or even hours to learn that.
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.
Stupidity: Right before the duel with Miss Fontaine, Jaden tells Jesse to sneak around and give the first aid to Blair. Rather than do exactly that, Jesse decides to stand behind Jaden and watch him duel for a few minutes, instead of going over to help her. He even repositions himself to be on Jaden's right, which would make it harder to get to Blair, even though his original position (on Jaden's left), would've made it easier for him to sneak around to her. (00:09:03)
Stupidity: In the original, the knight of the Phoenix suddenly appeared during the arena fights interrupting the show and stealing the Gold Cloth. In this remake of the saga, Sienna/Saori Kido leaves the arena by plane during a bombardment that occurs way before Nero/Ikki arrives to steal the Cloth. There is no reason why she would fly off in her VTOL without bringing the Golden Cloth with her, then (there's a lot of time for that). Instead she leaves it for the 4 Saints for them to "protect it", against a whole army and on foot in the middle of the desert.
Coming Home - S1-E13
Stupidity: Amuro's mom is horrified by him shooting at the two Zeon patrolmen, and says it's "wrong to point guns at people", but was apparently completely oblivious of him being now a soldier and did not say a thing about it when he literally landed in the middle of the camp piloting a jet fighter, wearing his full uniform.
Is Lupin Burning... ?! - S1-E1
Stupidity: Despite the fact that there are 100 (literally) cameras around the racing circuit and (again literally) everyone from the staff to the fellow racers works for the Scorpion gang, Jigen and Lupin's switch can happen without anyone noticing, even if it involved racing side by side for a lengthy period of time.
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.
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.
The Prison Prep School Murder Case File 1 - S1-E10
Stupidity: Paragon of cleverness inspector Adechi somehow did not check for any trap in the mysterious box he received, and brought it to a crowded cafe just, so he could show it to the kids. For the explosive trick to work, the puppeteer needed also to know exactly where Kenmochi would be seated and which seats would later Kindaichi and Miyuki pick, since the box had to be at such an angle that the puppet would be propelled to the exact spot on the roof that acted as podium.
It's Not Easy Being Green - S5-E16
Stupidity: Unless the tow truck was someone else's or Hank had the keys surely Dale and Bill could've used it to drive Boomhauer's car back.
Stupidity: Roberto Hongo is the center forward of the Brazil national team, and as we see from Tsubasa's poster/magazine, he did not alter his appearance except for wearing a fisherman hat sometimes. Despite being surrounded by football fanatics, he manages to keep a fairly low-key profile and it's totally not a big deal to have a top tier footballer hanging around the small prefecture.