+1
There are quite a few Human Centipede-related shocking scenes. I'd rank the second of the trilogy as the most shocking, and the scene in that which I often look away from concerns the breakage of legs, with gristle, cartilage etc lovingly focused on by the camera.
Todd Solondz film Happiness is one that features a lot of comedy - but what isn't funny is the scene where Bill Maplewood (Dylan Baker) explains to his child why he sodomized his drugged friend, and how much he enjoyed it.
An American Werewolf in London. Those friggen nightmares man. I watched this at the movies when I was young, and ended up kind of traumatized. The worst one is where we we see him in bed, eyes closed, peaceful - then suddenly he's this horror demon snarling. Yikes.
Saving Private Ryan - if it's that scary to watch the landings on Omaha Beach from the comfort of your living room, how the hell scary was it being there??