Julia Gets Her Head Stuck in a Fence - S4-E8
Stupidity: Once he decided to finally saw into the banister, all Anthony had to do to get Julia's head out was to saw through one of the thin posts on either side of her head. Instead, he saws through an enormous section of the staircase, later causing the governor to accidentally fall through. If he didn't realise that, one of the other designers, all who were looking on, should have. It's a lot to presume they all would have been that careless just for the benefit of a sight gag.
The Forecaster (No. 163) - S4-E10
Stupidity: Farnsworth tells Charnquist they've been compromised by a girl listening in on their phone calls and that Charnquist needs to take care of it. He is able to identify the girl, elude FBI, tries to burn his apartment down, is able to gains access to Maggie's apartment and knock out Aram in order to kidnap Maggie. He's a killer who works for someone who has arranged dozen of murders, and knows "take care of her" means kill her. There is absolutely no reason for Charnquist not to have just killed Maggie, Aram, and Fiona. He had opportunity and he ends up killing 3 cops in order to kidnap her and kidnapping Maggie would not have solved anything.
Stupidity: This highly prepared organisation knows Dracula is coming, but comes armed with guns they're not prepared to use, and allow him to grab a weapon and shoot one of them. Then they give him a tablet but assign the most basic of passwords to the Wi-Fi, rather than disabling it entirely, or even just giving him a Kindle, given the only point of it was access to books. Plot-serving idiocy.
Free Family Portrait Studio - S8-E24
Stupidity: Dwight is seen walking out of the bathroom with the diaper in the direction of the main part of the office in which Angela sits. If he was to try to stay hidden (which was obviously the whole point), he would have gone through the exit of the annex, waited until she was distracted/or hide it for later and Angela never would have seen. This was done because the plot required for Angela to notice but Dwight could have easily kept it hidden. (00:10:40)
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: Ahsoka is fighting against the spear-wielding woman. She keeps blocking the spear using both her sabers. It would be very straightforward to block the spear with just one lightsaber (as she proves she can do just as well after she loses the smaller one) and use the second one to, for example, cut off the woman's hands.
Suggested correction: This is opinion, not stupidity.
Stupidity: The Evans family are living in the projects of South Chicago in the '70s, but their front door is always unlocked.
Will the Real Martian Please Stand Up - S2-E28
Stupidity: The whole plot is based upon 6 people not being able to spot the seventh (odd man out). We can eliminate the couples, the driver remembers the pretty blond getting on the bus and the crazy old guy would stick in anybodies memory, so it leaves only the sour old guy in the coat and hat as the martian.Also all the troopers has to do was ask for IDs which they do but quit after they ask the crazy old guy for his.
The Clean Room Infiltration - S8-E11
Stupidity: On the way home from the university after wiping their names from the sign in sheet, Leonard, Howard, and Raj are all singing Jingle Bells. Leonard is driving and has his eyes closed all the way through singing the song, this makes no sense at all giving he should be looking where he's driving.
Stupidity: Dexter's decision not to kill Trinity when he had the chance eventually led to Rita's death, a mistake Dexter told Deb he would never make again. However, at the end of this episode, he decides to spare Oliver Saxon so Deb can arrest him. Dexter doesn't stay to ensure that Deb successfully has Saxon in custody, which leads to Saxon escaping his shackles with the unwitting help of Deputy Marshal Clayton, and shooting Deb before leaving the scene. Dexter therefore does make the same mistake again.
The One With All The Rugby - S4-E15
Stupidity: Emily tries to help Ross inflict pain on the other rugby players and tells him about one player who doesn't wear a cup. No one who knows rugby would ever wear a cup, it is more hazardous than helpful to wear a cup in rugby as it involves a lot a grinding, and a simple slip or movement could cause serious damages to the male genitals. Especially if these guys are British and well versed in rugby which they are.
Stupidity: Whilst Reva is running across the rooftops, there is a moment where she does a backflip in order to propel her forwards towards the next rooftop. If she was attempting to jump between roofs, then doing a backflip would not have been useful as it would only slow down her momentum instead of build it. (00:25:28)
Halloween 2: The Ghost of Hetty's Past - S2-E5
Stupidity: If Sam was so worried about conserving oxygen, she should have blown out the candles in The Vault.
Stupidity: When the bad guys are discussing the plans inside a private jet, the scene finishes and there's a shot of the plane in the sky. The plane immediately veers to the right, and spins almost 90°, as fighter jets do when they turn quickly. If there were three people inside, (one of whom was in the bathroom) they would have been thrown about the cabin quite violently. (00:11:25)
Stupidity: When Franklin and Tara are hooking up at the motel, it appears that sunlight is shining through the windows. Franklin is unaffected.
Stupidity: Donna runs in to save everyone from the collapsing pylon, dying in the process, despite the fact that Superboy or Raven, both more powerful/resilient, could have stopped it falling without any issues whatsoever. Not even like anyone was distracted - the fight was over, they were all just standing around.
God Complex - S5-E23
Stupidity: Maggie and OA are searching the building. As they walk up the stairs, Maggie is using the Harries technique, but she has both her handheld flashlight and the gun's flashlight on at the same time. This defeats the purpose of the technique. Additionally, it's daytime, so the building is lit up from natural light sources, but they still have their flashlights on. (00:13:36)
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.
Snow White and the Seven Bradys - S5-E3
Stupidity: When the kids all pick the random-shuffled papers to choose which kid will be which dwarf, it NEVER occurred to them that with six kids and seven dwarfs they would be one short. This was only discovered once Peter (the last to pick one) was now up for a turn. How did nobody figure that out before the name-choosing even started?