A Bad Reflection on You - S1-E38
Stupidity: The decision to risk revealing their identities to Bulk and Skull is one that the Rangers could have easily avoided. Since they tell the bullies to cover their eyes and ears, under the false pretense of a magic trick, they could have simply teleported to the Command Center, or any other secure location, and then morphed, well away from prying eyes.
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)
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)
Stupidity: The last remaining Xindi, in desperation, attempts to release the virus over the fan, despite the virus not being fully ready. However, it seems the only reason he didn't release the virus at that time was he had to seek cover from Archer and T'Pol shooting at him and to start shooting back at them. However, he had plenty of cover from the rooftop stairwell, which was right next to the fan, and he had enough time to dump out the contents over the fan.
Storm Before the Calm: Part II - S1-E38
Stupidity: Shane could have easily avoided the blast from Lothor by simply flying away to dodge it. Instead, he just hovers over him and allows his Battlizer to be destroyed.
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.
When in Rome - S1-E3
Stupidity: A supposedly covert camera is placed in plain sight on a wall in a crowded room, with a prominent antenna showing, and a blinking blue light. (00:16:55)
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: Andor and Luthen set a vehicle to drive and distract the security team. The vehicle is destroyed, and they immediately round the corner in full view of the team on a speeder and drive away, then blow up the vehicle. They could have driven away on any number of other streets without revealing that they weren't in the vehicle, keeping their escape secret. And if they blew it up before the team looked too closely they might have even been deemed to have been killed in the crash.
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)
Worlds Apart - S1-E2
Stupidity: The bad guy kills the deputy in the swamp, then later sees a little girl who witnesses the killing run away. He then searches the boat for a weapon and runs off after her after he finds a machete, without even considering the officer's gun still in its holster. Abby proceeds to make the exact same mistake later when she finds the dead officer (meaning there's danger nearby) and hears the girl screaming and runs in the direction of the screaming without taking the gun to protect herself.
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.
Stupidity: With one humongous stretch of luck (Magnum loses the guy he is looking for but TC who just happens to be generally 'in the air' is close for him enough to just be able to do air recon for him, and spot the guy who is still running because he must have gotten take-away food from half a city away on foot), Magnum arrives so close to him that they are in the same street maybe 10 meters apart. Yet Magnum needs another tip from TC and his passengers to spot him getting inside a house, something he could have never missed. (00:16:00)
Stupidity: When Jonas says he saw a creature go through the walls, people want to assume he must be hallucinating. Yes they sweep the base, but Carter questions its ability to pass through solid matter as if she's never seen that happen. When Jonas sees a creature again on the device with Carter there, she gives a look like he's going crazy rather than at least try to use a TER to scan for it. Plot wise it seems this is done just so O'Neill can leave the base and spread the "infection."
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."
The System - S1-E2
Stupidity: The plot hinges on the fact that even Frank Marley's most trusted man would doubt him because of his actions, but he and Marley counted the money together; he should know that Marley was right and the amount declared was not lower than the actual money deposited. Instead, he is fooled like everyone else by the extra 25K$ planted by the IMF team. Their plan can't work unless he is oblivious and/or forgetful.
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.