I think ‘Disturbing’ as another genre all together, i love watching all the horror classics mentioned but stuff like Irreversible, Salò, or 120 Days of Sodom, or Martyrs etc are just horrible to watch. no fun at all.
Funny Games (Haneke original) is another one that really had an impact on me!!
I think when it boils down to raw human cruelty rather than ghosts and vampires, that reality can be chilling! Snowtown was another!