Half Life 2. I'm no pussy by any means, but there was something about that game atmospherically that didnt agree with me. To this day I don't know what it is, but I found myself inching and moseying everywhere constantly looking all around me because I was so on edge. And at a certain part of that game (headcrabs, zombies) it gave me a really eerie feeling that I couldn't shake and I never got past it.