Poonga's got a good list, and Private Lessons was one of my "You going out tonight Mom? Be home when the bars close? Oh don't mind me...I'll be FINE!" late night HBO favorites as well.
A couple of other unmentioned goodies:
Up the Acadamy
Hamburger: The Motion Picture
Joysticks (c'mon people! No one HERE mentioned this one??)
Decline of the Western Civilization (both parts but especially part 2).
Moving Violations (not trashy but damn stupid)
Losin' It (Tom Cruise's first movie. Bad bad bad)