Reddit mentions of Naked Lunch, 50th Anniversary Edition

Pretty much anything by Chuck Palahniuk.

• Haunted is probably the most flabbergasting, but it's so off the wall and unrelentless that after awhile you'll probably become numb to it.
  
• Survivor involves an interesting look at fictional cult behavior. As a bonus, it's also full of everyday household cleaning tips ("Remove protein stains (esp. semen) from clothing with cold salt water then wash as usual.", "Clean up small shards of broken glass using a piece of bread.", etc.)
  
• Diary is about art school, conspiracy, and material excess. Not the most disturbing of his novels unless a critique on suburbanism would scare you (it did me).
  
• Fight Club, I assume, requires no explanation. It's worth reading if you've seen the movie.
  
• Choke is another that's been adapted to the screen, so probably doesn't need an explanation. But for the record, I found it more amusing than disturbing.
  
  edit: Also, American Psycho by Bret Easton Ellis, Naked Lunch by William S. Burroughs, A Clockwork Orange by Anthony Burgess. And The Road by Cormac McCarthy, but only for one scene around the middle... anyone who's read it knows what I mean. Other than that, I found it to be a very emotion-provoking novel, but not "disturbing" in the sense that I think you mean.