I can't believe this hasn't been mentioned yet. Pretty much every freaking scene in
Pink Flamingos. I had gotten into a similar discussion with my college roommate my junior year of college. I had stuck with my guns and said that SE7EN was the most disturbing, shocking movie on Earth. He then countered with Pink Flamingos, a movie I had never heard of. After being forced to sit and watch the movie, I soon learned what a disturbing movie it was, and how demented John Waters really is. :p
The worst scenes were the "singing anus" scene, the "chicken" scene, or the scene where Devine eats a pile of dog shit.

Then again, pretty much any scene in that movie is shocking and disturbing. :barf: