I am a big wuss when it comes to scary games. I hate them. The only time I can barely play them is if they are frikkin' brilliant, and/or if I am invincible. That takes some of the sting it seems. Oh, and with the sound on low.
When I tried out Doom 3 I only played it for five minutes. Being jumped twice, then I just turned it off. Never played it again. I almost beat FEAR, but then my computer broke and I had to reformat. Never again.
I played the demo for Condemned. Was enough for me.
But the most pants wetting moment, without actually being pants wetting, was Alien V Predator. Playing as a Marine. I had just started playing, everything is dark, and the motionsensor shows no movement. I walk forward. Nothing. Then something moves. I turn on the flashligh. Nothing. Switch to motion. There is something in front of me. I shoot in panic. A lot of movement. Flashlight. The movement turned out to be a lamp or something, which broke when I shot it, so all the glass showed up on the sensor. I took a relieved breath, then switched to the sensor again. Now there was even more movement, and it was scattered. Coming for me. But I heard nothing. When it was more or less right on top of me, I looked up with my flashlight. There is one alien just waiting to attack, so I shoot it in panic. As it falls, I follow its body as it falls, and out of the darkness another alien lunges at me. I quit and never played as marine again.
(This is some time ago, so might remember it wrong)