Crobat's Fear-Induced Retardation Syndrome.

This widespread syndrome is known to only affect individuals within horror/thriller movie plots. It is characterised by a complete loss of rational faculties, memory lapse, and an inability to maintain one's nerve.

Seriously. Have none of the people IN horror movies actually WATCHED a horror movie in their lives? I point my finger particularly at the teenage/young adult characters. So, all characters in all horror movies. You've all got some explaining to do.

No one is so removed from pop culture that they've never had the pleasure/misfortune to watch something truly terrifying. With that in mind there are a few things you tend to pick up. Like the ever golden "don't split up" rule. Or even better: "don't investigate that dark room alone". When you hear something, anything, any noise at all, you do not go look alone. Usually the sounds you hear are less than benign anyway: a scream, a snarling animal, dull metallic thuds and/or scraping. Do you still really feel the need to investigate? Really? Fine, go get disemboweled. What do I care? Moreover, you kind of agreed not to split up about half an hour ago. Look, I don't care how big the cheerleader's chest is, don't be a hero. Keep your trap shut, eyes forward.

Of course, they can't all be blamed: some rules are a little harder to understand. My personal favourite is what I like to call the stairs paradigm (not really, I just liked that syntax and needed some wanky bollocks to fill it). Essentially: don't go up the stairs, and don't go down the stairs. Odds are there's something on the second story of the house waiting inconspicuously. After all, you've cleared the ground floor, so you can only assume that the above-ground floor is safe as well. NO THAT'S JUST WHAT HE/SHE/IT WANTS YOU TO THINK. If you're already upstairs, it's probably laying a trap downstairs. "But the staircase leads right to the front door." Oh, if only it were so simple, you simple simpleton. Expect the worse and then some. Seriously, stay away from all staircases. They're horror movie disaster areas.
Don't be a minority. Don't be a minority of any kind. Don't be a social minority, don't be an ethnic minority, don't be a religious minority, don't be a fucking minority. Minorities are expendable. The writers need well-adjusted, straight, agnostic/vaguely-Christian Caucasian males and females to survive.
God damn stupid bitches in horror movies.