I've turned off many a film because it's been so awful but sometimes you sit through an entire film to the very end expecting something to happen. One such film is 'Gerry' starring Matt Damon who I love but that film has to be the biggest crock of shite ever made.
The Room (2003) Without a doubt the worst movie I've ever seen. But, also falls into the it's so bad it's not even just good, it's incredible category. There's an entire fandom built around it. Highly recommend you check out some clips on YouTube.