Guinea Pig: Flowers of Flesh and Blood.
Essentially, a bird gets drugged and kidnapped, strapped to a table and cut to bits.
Charlie Sheen was once given a copy and when he watched it he thought it was a real snuff film and contacted the FBI !
Its gory and sickening so it's not going to make you jump out of your skin, but its only about 40 mins long so wont take up too much time :)
Other good shouts are Eraserhead, The Brood, Rabid, - basically any Lynch or Cronenburg film if you want disturbing.