The most disturbing movie I've seen (so far) is Funny Games, which I saw when I was like 15 or so. I think the young age might have been why it is still imprinted in my memory with such fear and disgust. The movie is about two young men who takes a family hostage and then slowly goes about killing them. The entire movie is just disturbing and the final moments fills you with a sense of dread that sticks with you for a very long time. Part of me wish I could unsee it, other parts of me is in complete awe of the creators who made me feel something so intense from fictious moving pictures.
Trailer:




















