Twilight.
I wish I could say Twilight was the worst movie I've ever seen, but I'd be lying if I did.
In all honesty, I'd probably give Twilight a 6/10. The effects were iffy at times, Kristen Stewart couldn't act her way out of a wet paper bag, and a some of the dialog is really cheesy. That said, the movie tells a coherent story of forbidden love and is a largely faithful adaptation of the source material, which is more than even some of the Harry Potter movies can claim. I'm looking at you, Movies 3 and 4.