Running upstairs when the killer chases them. Where are you going to go once you reach the last floor?
And, as has been mentioned, going alone and unarmed to investigate something clearly dangerous.
If you get warned, then you follow it. Don't go all "wow theyre stupid" and continue on your merry way! Theyre warning you for some reason! Oh and god damn it, if you are in a kitchen and there is a KNIFE five feet from you, GRAB IT. I know he's coming after you, but still does it take so long to grab a bunch of knives and run. I mean you never know if running will save you (which most of the times it doesnt)
When the hero/heroine shoots the killer then stands there crying or shaking about it instead of running away... =_= Don't fall to the ground next to the killer, run away!! Double tap then run!
The biggest and stupidest mistake ever made is going up the stairs and not out the front door. Whenever I see the character go up the stairs, I scream, "NOOOOOOO!!!!" But I think, "you are soooo dead, stupid!!!!!"
1: Doing it. It just never ends good. I guess its because it distracts them.
2: Screaming and running when they face the killer instead of kicking his ass. I mean seriously what is that??? Don't you guys have hands and feet to defend yourselves?
3: Going to roadtrips or camping in deserted places. This is like begging for your death.
4: Trying to save someone else.
5: And yes, going upstairs. Except if you're trying to jump out of the window, it doesn't help.
When they either go into a basement without a weapon or torch to investigate a noise or when they run upstairs cause when ya reach the top floor where ya gonna go out the window?
Jennifer's Body-girl getting a ride with random strangers. Which leads to becoming a demon and eating people. And dying.
And Soon the Darkness-If you knock out the guy trying to rape/kill you, you don't leave his unconscious body there, you KILL. HIM.
Multiple-OH MY GOD HES CHASING AFTER ME! OH MY GOD I GET INTO MY CAR! OH MY GOD I DROPPED MY KEYS! OH MY GOD THE KEY BROKE! you can just see all of the "Oh My Gods" on their face during those scenes.