Not movies that are "so bad they're good" or low budget films that have some camp value, but movies that are just incredibly bad, to the point their very existence offends you.
I'll start with a few:
- Crazy, Stupid, Love - the scene where Gosling and Stone spend an extended amount of time giggling on a bed and talking about Gosling's money is one of the most insincere and highly nauseating representations of humanity ever
- Star Wars Episodes II-III - while The Phantom Menace is boring, the acting is better, the story is passable, and the film doesn't in any way ruin the original trilogy. II and III on the other hand fail on almost every level
- 2012 - has any other movie of this magnitude been made so irrelevant so fast?