8mm, without a doubt. It was both disturbing in what it depicted on the screen, and in the fact that the movie accomplished nothing else. Unlike Se7en, or other similar movies, it had no real purpose other than to disgust the viewer.
I walked out of that movie, and it was the only time I ever asked for my money back. Graphic violence and nudity don't bother me when they are just a part of the movie, but 8mm existed only to show the violence and nudity.