Requiem for a Dream. I asked a friend for a recommendation that would be bleak enough to suck all the joy outta my soul, and this nailed it. Ellen Burstyn was incredible.
'funny games' if you're looking to remove more joy from your life down the track. there's two versions, an austrian version off the top of my head which is my preference, and a shot-for-shot american remake. has naomi watts.