I remember a lot of plot, but Google doesn't help! Two teenage lovers are on a road trip. A slightly older guy (twenties) spies on them having sex, masturbates and eats his own semen. He joins up with them, leading them into a crime spree where they decapitate a Korean store owner while robbing his shop. The decapitated head continues to talk for hours (they see this on the news). They manage to piss off some skinheads along the way (I can't remember how). Eventually the skinheads catch up with them and castrate the guy from the couple.
At one point, the girl tells the older guy he's just a 'life support machine for a ' or something very similar.
I swear to god, this is a real movie. I don't even particularly want to watch it again, but I must know what it is?

The Doom Generation (http://en.wikipedia.org/wiki/The_Doom_Generation)