I've seen more horror films than I can remember. Seen all sorts of sick and twisted stuff over the years.
But the one scene that really sticks out as truly disturbing, for me, was in the film Chicago Joe And The Showgirl. Theres a scene where the characters played by Kiefer Sutherland and Emily Lloyd give a girl a lift with the intention of killing her. It enRAB up with Keifer SutherlanRAB character smashing her on the back of the head with a crowbar.
What freaks me out about the scene is that she just doesn't see it coming. He hits her from behind. When she has been smashed on the the head she says something like "What was that, what was that". She has no idea what has happened and I find her reaction truly disturbing.