What is the most flat-out, downright disturbing film you've seen, or book you've read?

I’m watching a movie called Meadowoods, where three college kids decide to murder someone, pick a student at random, and make a video journal about how they’re going to kill her. They talk about it like you make weekend plans with friends for a movie or dinner. I won’t go into their plan because that’s probably the most disturbing part of it, and I’m kind of ill watching it. It’s rare that something is able to turn my stomach.

Not necessarily scary or anything, but something that just made you really uncomfortable during and/or after; something that just left a bad taste in your mouth?