Stupidity: Arashi tells Hoshino through his radio to call the HQ, but as shown several times throughout the show, his radio is perfectly able to do that directly himself. Even in this very episode later Hayata uses the standard issue radio to let the HQ hear the alien's requests. (00:07:20)
Stupidity: With about 5 minutes left, the Black Sheep fly towards a Japanese carrier. They are flying Japanese planes. The Japanese spotter speaks in Japanese. The translation on the screen says "There ours" instead of "They're ours."
Stupidity: Some ancient advanced civilization took to the task of building this amazing net of stargates that enables instantaneous traveling over hundreds of light years or more, but any stargate can be disabled by anybody just by covering it with dirt or rocks. Apparently if the stargate is buried then it becomes inactive. See Season 1 EP.1.
Suggested correction: This is just you having a different opinion on how the Stargates should work. In fact, the ability to make a Stargate inactive by burying it is a brilliant move by the Ancients. Burying the gate, or even creating a barrier, prevents enemies (like the Goa'uld) from having a convenient way of invading a planet. Although some races, like The Nox, show the ability to activate a Stargate without having to form an unstable vortex.
Firefly, Light My Fire - S1-E1
Stupidity: The button Benita uses to open her trap door also turns on/off the record player and swings the record arm.
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.
Suggested correction: Superman knows the 'strong bad guy' is close to his own strength. After fighting him, he knows what effect the crash through the wall would have had on him, if he was knocked out, and how long he would be out for. So he knew there was little risk of the guy coming around in 10 seconds. Alternatively, he X-ray scanned the area and saw the guy was no longer there.
Who, What, Where, Wendigo? - S2-E10
Stupidity: Dwight, Audrey, and Nathan all know Dwight's trouble is that all bullets are attracted to him, so why is he with them when they go looking for the killer, knowing every one is using a gun?
Stupidity: Linda suffers a gunshot while in the hospital. The doctor calls for a trauma team that responds immediately to take her to surgery. The next time Linda is shown the trauma team is still taking her to surgery through the hospital hallways, and the whole Reagan family made it to the hospital and in the hallway as Linda is being taken to surgery. The hospital hallways must be long or the trauma team took the long way to surgery to allow the family to be there. (00:03:28 - 00:05:57)
Black Butterfly Murder Case: File 1 - S3-E1
Stupidity: Since "Touno" was prominently featured on the photo of a lengthy article about the butterfly crypto-entomologist Shimon Madarame, it's quite strange to say the least that Kindaichi and his journalist friend wouldn't have the slightest clue about his name or generic occupation. Generally a magazine does not put a person in 1/3 of a double page spread without at least hinting the reader about a person's identity, especially when they are not doing anything in the picture.
Stupidity: The Resistance is a rescue team that helps the various protagonists escape schools. They do this by leaving intricate hints that lead to a detour to the school alarm instead of going straight there, setting off the alarm and rescuing the protagonists.
Chapter Eight: The Battle of Starcourt - S3-E8
Stupidity: SPOILERS AHEAD: It has been a good minute between Hopper killing Grigory and Joyce turning the key. He could have used that time to run as quickly as he can towards her, instead of staring at her for 30 seconds. Also, Dustin didn't have to yell (through the radio) so panicky yet about closing the gate. While Mind Flayer was killing Billy, El and other kids could have used the time to run further again and get another 2-3 minutes, in that time Hopper would surely come to a safe place.
Stupidity: Hungarian Police Lieutenant Benedeke Erdös has broken right arm in a cast. Although his arm is in a cast, he is still in uniform and carrying his firearm in a holster on his right side. There's no way he can draw the weapon or secure it. (00:20:45 - 00:21:19)
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.
Stupidity: Harold isn't sure whether to trust the flash drive Claire gives him, worrying connecting it to his laptop will send Samaritan all his personal connections. Somehow it doesn't occur to him to just use a completely disconnected / airgapped laptop, in a Faraday cage or similar like the one he kept Root in. If the flash drive had malicious code on it, nothing could be transmitted anyway.
Emohawk - Polymorph II - S6-E4
Stupidity: On the walk back to Starbug, the Emohawk jumps on Lister's head to disguise itself as Lister's hat, but it leaves itself in its natural form whilst the crew continue to walk. The Emohawk is supposed to be disguising itself to fool the crew into making them think it is any everyday object. The Emohawk eventually changes into Lister's hat, but leaving itself in its natural form even for just a small amount of time could blow its cover. (00:18:15)
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)
Invasion of the Punk Frogs - S2-E8
Stupidity: Shredder uses a holographic projector to appear as a normal person. He could have just taken off his armor.
From Injustice Came the Way to Describe Justice - S1-E5
Stupidity: The police raid an apartment in search of guns. They should have used a ballistic shield for the point man to make entry and hit the apartment with a concussion device (flash-bang). The police officer who took a stomach full of lead would have more than likely survived had they been properly equipped. Ballistic shields have been around since 1977. This story takes place in 1992. (00:49:17)
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.
A Rough Whimper of Insanity - S1-E7
Stupidity: The hacker's VR goggles are not plugged in to anything (despite having a wire for this purpose) when he and Tom sit down at the computer in the teacher's house.