Pink Flamingos. But, seriously don't watch it if you can easily get sick to the stomach. It's not gorey or anything like that. It just contains some pretty raunchy scenes. It's a John Waters' film, if you're famililar with him.
Basically it's about a family who strive to be the "filthiest" people around, and they certainly live up to it.
It's not a mindfuck per se, but it definitely fucks with your mind. Don't watch near the elderly or children.