The Whole World Is Watching - S1-E4
Stupidity: The Dora Milaje arrive to take Zemo. John calmly attempts to talk them down, but it leads to a huge fight when he puts his hand on Ayo's shoulder. There are multiple instances during this fight where they totally would have stabbed John and Lamar with their spears, and are only stopped because Sam and Bucky intervene. While it's understandable they would want to obtain Zemo, attempting to kill two people to do so is completely out-of-character and goes against all of their morals and principles.
Suggested correction: I watched the scene and I never saw any of them try to straight up murder anyone. They were very skilled and precise in their attacks (for example, pinning John) and wouldn't have murdered anyone.
Here's a link to the scene (https://youtu.be/cpUq-kYMPkc). I counted three times when they almost kill them. First, after Ayo knocks John to the ground after he puts his hand on her shoulder, she attempts to stab him with her spear, prompting John to pick up the shield to stop himself from getting stabbed. There is no way she could have known that he would have picked up the shield, and if he did not do that, she would have totally stabbed him.
Second, there is another attempt where Ayo tries to stab John, which is only avoided because Bucky grabs onto the spear with his metal arm. Third, the two other Dora Milaje get into a fight with Lamar, and there is a point where one of them is about to throw her spear at him, but Sam grabs onto the back of the spear, so she cannot stab him. These are clear attempts to kill John and Lamar and were only avoided because Sam and Bucky intervened.
Stupidity: The inspector knows that his house has been bugged; he does not know how many bugs and cameras are there, he just knows there are some. He does find a bunch of them with great ease when he gets back home - making you wonder how could he have ignored them to begin with, since all it takes is for him to raise his eyes, they are fairly big black cameras who do not camouflage at all for the most part. He then proceeds to make a phone call to the big baddie from his landline. Nobody in their right mind would do such a thing. Heck, you wouldn't want to use your home phone for such a call even if you didn't know that someone just put bugs all over your house.
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.
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.