AVGN: Front door, closet... front door, closet... closet.
Cracked blog once poked fun at Terminator, specifically how all these people were clearly either terminally dumb or seriously determined to self-terminate (sorry). That is —
Cyberdine's tech support engineer: ...Again, my strength really lie in fixing computers, not in designing or managing needlessly nightmarish robots, but it just seems like a basic rule of computer-making that you should be able to turn it off at some point. I mean, my toaster has a plug in case something goes wrong, you know? And i haven't armed my toaster or given it access to my house's security system.
Pretty much half the population of Klay World is at any given moment doing something that will most likely result in their death.
J from Marble Hornets has made such brilliant decisions as, after being attacked when he visited an abandoned house, immediately deciding to return. Then announcing when he would do so to the internet at large. Totheark, who J thinks is the attacker, responds with a video that basically amounts to, "Yes, please come so we can eat you!" J still goes. At night.
And taken to new heights in Entry #40, wherein J gets tired of waiting for Alex, so he decides the best idea is to go for a walk in the creepy haunted woods. He had never been in the woods before, didn't know his way around, and, needless to say, didn't tell anyone where he was. On the plus side, he then did the most sensible thing anyone in the whole series has done so far: When Slender Man shows up to say hi, J just drops the camera and runs.
The Interviewer guy of On the Set of 4th Edition normally is a Cosmic Plaything, getting killed by the creatures he interviews that don't get killed alongside him. But when drunk, all survival instincts flee him at high velocity as, to demonstrate a skill challenge, he decides to hit on The Lady of Pain, who he knows is capable of nullifying gods and flaying people with a glance, and he outright tries to intimidate her into giving him her number. Of all the times he's been killed in these shows, this was the one time he deserved it.
About 99% of the people in the trailer in the fakeShark Pool movie. A giant, man eating shark has somehow ended up in a swimming pool...and yet they don't just stay out of the pool...which the Only Sane Man repeatedly suggests they do.
Shrooms has Red; he believes the right way to drive ghosts from a haunted house is to insult their originality.
February, the schience officer from Starship who goes down to an uncharted alien planet and scans the air for breathability... after taking off her helmet. It gets worse from there.
Crops up from time to time in Survival of the Fittest. One of the most notable examples was the very first death in v4. Danya tooks pains to tell the students that the collars were more sensitive this time, and not as prone to tampering. This does not stop Remi Pierce from attempting to slice off his collar with a knife the second he woke up on the island, with expected results.
Toad often makes mistakes that cost him and his friends their lives. Examples are concentration of constipation  when he doesn't drink enough water for the pills and inflates, and at the end of the Christmas episode  when he slathers gasoline on the Christmas tree, which causes the tree to ignite and explode.
Team Service Announcement: The BLU Heavy in Minigun Spinup takes so long to walk anywhere with his revving Brass Beast that the RED Spy and Sniper decide assassinating him is just too easy to be fun. So instead they drive a steamroller over him.
The BLU Soldier in Grenade Launcher willingly stands on a stickybomb trap, claiming "I got a good feeling about this!"
The Flying Man: Rob, the Dirty Cop who's dealing weapons. Sure, the Flying Man's been ruthlessly tracking down and murdering criminals for a week, but there's no way it'd happen to him, right?