Day 4: 11:00 P.M.-12:00 A.M. - S4-E17
Stupidity: When the couple is in the plant they call Jack on the cellphone, he instructs them to open the case and separate the book from the activation device. This was stupid, he should have told them to destroy it, since the codes had changed the moment Air Force One crashed, and it would take about 1 hour to make this work. This is explained later on in the show.
A Deadly State of Mind - S4-E6
Stupidity: In the final scene: Columbo lays a trap for the murderer (George Hamilton). The 'eyewitness' when Hamilton fled the murder scene was a blind man. Hamilton is aware of this. Columbo's gambit depends on Hamilton's assumption that Columbo has coached the witness to act as though he was sighted so as to convince Hamilton that there is evidence against him. In fact, Columbo has the witness' brother, who is sighted, pretend to be the eyewitness and identify Hamilton as the man he saw driving away. When Hamilton falls for Columbo's trap and, believing he is in the presence of the blind man, tries and fails to 'prove' the man can't see. By doing so he reveals his knowledge that the witness was blind, incriminating himself. The problem is, that only a minute or so previously, Columbo had placed Hamilton under arrest, and failed to read him his Miranda Rights. Considering that Hamilton's slip up is the ONLY evidence Columbo has against Hamilton, this was a spectacularly stupid move on Columbo's part. Regardless of how many officers were present to witness this, the fact is that Hamilton was under arrest and had not been advised of his right against self-incrimination; meaning nothing that he said when under arrest can be used against him.
Stupidity: Al tells Peg to hide the meat and cheese tray from Bud and Kelly. Obviously you need to refrigerate meat and cheese yet Kelly says I swear I smell cold cuts. Do we have any? Al and Peg both say no. They both have to see it in the fridge every time they open it.
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.
The Killer - S1-E1
Stupidity: To make the hit, The Killer places a bomb on the ceiling of his room - which is the floor of the victim's. He has absolutely no way to know where in the room the man will stand and when we see the explosion, it does not even touch the couch. The brilliant plan of the flawless killer is anything but brilliant or flawless.
Stupidity: Why do they always have to go through that washing machine setup in the laundromat when they have a great functioning elevator to the lab?
Suggested correction: Why would Gus go through the process of hiding the lab entrance stairs behind a washing machine but leave access to a freight elevator wide open? The elevator would be just as hidden and probably locked up. Not to mention it would be slower to take than simply walking downstairs.
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)
Log 81: The Long Walk - S1-E14
Stupidity: They are looking for a red convertible. No other description of the car. A red convertible pulls up behind them and passes them. The ragtop roof is up but it's still matches the description. Doesn't faze them in the least.
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.
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.
Stupidity: When Eddie finally finishes installing the VCR and it explodes, they get a man out to repair it. However, Eddie had previously told Richie that he'd stolen 60 VCRs; 17 in the living room and another 43 in the attic, so they could have used one of the other 59 and saved themselves a crate of Malibu.
Stupidity: Characters repeatedly make note of how hard to kill the Wraith are, but sometimes, especially in the final episode(s) of season 1, they go down easily in a few bullets each, and then don't even regenerate as the characters turn their attentions elsewhere.