They don't have to be the worst, just ones that make you want to smash the screen when they're on.
For me the ultimate one is Love, Actually. I'm sure it's very passable romance bilge. But I've seen it about a dozen times now through no action of my own. I honestly hate it. I want to burn all the dvds of it.
Like, when that Andrew Lincoln character does his emo-Dylan impression at Kiera Knightley's door, gets a kiss for it, then sods off...and then the next we see of him he's got a girlfriend! So his plotline through the film basically fleshed him out to be a peeping tom who tried to wreck his best friend's marriage and then shacked up with some random extra at the end of the film. Deep, man.
I know it's not a real reason but the entire film just makes me angry.
My boss hates Lost In Translation as he feels it's a racist pile of shite, which is at least a better reason. I've never seen it so can't comment.