Stupidity: Paulie and an associate just killed 2 drug dealers or stash house guards, and they are rummaging throughout the apartment touching appliances and other surfaces without any gloves. Paulie was previously arrested and did time so his fingerprints are on file. Paulie also used a knife to stab one of the Colombians without any gloves on, and he just left it in his body. The police would have no problem linking him to this crime within a week after forensics did their sweep. (00:03:00 - 00:04:17)
Stupidity: The brothers are angry at Leo because they say he's responsible for them dying because he chose to save other soldiers instead of them, Leo also blames himself for the same reason and says he should have stayed and gotten them out. But in the flashback it shows Leo helping them and then running off to help other soldiers, after he runs off the brothers are killed just a few seconds later. Even if Leo had chosen to stay with the brother he couldn't have gotten them out in time, the only difference would have been Leo would have died with them, but Leo dies in the same war so he didn't live much longer. Leo's guilt and the brothers' blame don't make any sense at all.
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.
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.
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: 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.
The Prison Prep School Murder Case File 2 - S1-E11
Stupidity: Akechi finds the pieces of chalk but does not investigate the open locker, where the victim left what turns out to be literally the name of the murderer. The plan of the all-knowing Puppeteer works only because the smart investigator does not perform even the most basic crime scene.
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: 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.
The Night of the Firebrand - S3-E2
Stupidity: West is introduced to, then knocked unconscious by Vixen as she hides a club behind her back. A trained Secret Service agent like West would not have let his guard down in this situation, as the entire fort was awash in bad guys.
Stupidity: The Chief Baker on the Titanic is fast asleep in his bunk when the ship hits an iceberg. It is said that he survived because he drank heavily prior to his going into the water. He had at least a full tumbler of alcohol. He is shown drinking it in two scenes. He is shown dressed in full white chef gear and even wearing a white chef kerchief. It seems stupid that he would wear such a thing if he had just been startled awake.
Zorro's Ride Into Terror - S1-E8
Stupidity: When Diego sees that the passage door is opened, he invites Sergeant Garcia to sleep in his bed. However, Diego never tries to close it, and during the rest of the scene, nobody (even Captain Monasterio) seems to see it open.
Stupidity: When Brass and Sarah enter the locked storage cellar where the boys are hidden, Greg, a graduated rookie, straggles along behind them when he should have known better to stay put. As anyone could have come along and locked that cellar door behind them, trapping them inside.
Through the Valley of Shadows - S2-E12
Stupidity: Burnham and Spock find one person alive from the otherwise-dead crew, miraculously. They know Control can infect humans, they know how advanced it is, the entire setup screams "trap", and yet they don't even question whether Gant even might be under Control's...well, control. A simple scan would have turned up anomalies and they could have avoided what followed.
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)
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)
Stupidity: During the scene at the restaurant, Rose pulls the fire alarm. Then she and the doctor run through the kitchen, past several chefs who just duck and crouch into corners. This would easily be one of the stupidest ideas ever. If there was a fire, they would evacuate out the back door instead of just sitting there waiting to be choked to death. And if they knew about Auton Mickey, running out the back door would also be a lot more logical than just crouching down and waiting to be battered to death.
Stupidity: When they are conferring before surgery everyone is keeping scrub except for Avery who has his arms crossed. Shortly afterwards you can see him look around at all his co-stars, realise he screwed up and try to casually raise his arms. (00:15:00)