@Whirls -- Happiness is quite the amazing film, both in its ability to present some of the darkest comedy known to humankind and make one feel at unease with humanity. Todd Solondz has made some absolutely amazing subversive films, all involving subject matter that is unseen in most films, even in the independent circuit.
Also from Solondz (and none of these can be considered "bad," by the way):
Palindromes (2004) - Because nothing says "great movie" like child sex.
Storytelling (2001) - Your answer to the questions, "What is it like to see a college girl have sex with a guy with a physical deformity go on to have sex with her black professor?" and "How can we turn a normal ten year old boy into a cruel, heartless, nearly-evil piece of shit?"
Welcome to the Dollhouse (1995) - Teenage awkwardness at its finest. This is actually considered a classic by many.
Palindromes is actually -hilarious- if you can stomach the rather lurid subject matter.
@Iggy & Rynostar: I've seen the MST3K version of Santa Claus Conquers the Martians, and even sitting there watching them make fun of it was painful. Oh, but when the "polar bear" comes and attacks--priceless.