"John Dies at the End"
First it starts interesting, two guys find a mysterious drug which gives them incredible mind powers like speaking to the dead, predicting the future and seeing things from other worlds, yet the drug is evil, kills people and makes them see things they shouldn't.
But then it goes downhill, and turns into an insane mixture of horror, gore, science fiction and bad comedy that makes absolutely no sense whatsoever. It's like Evil Dead on crystal meth, if Evil Dead had aliens, drugs and alternate universes in it.
Consider watching only if horribly stoned.