Worse than Manos the Hands of Fate
I didn't think I'd ever say this abour any film, but a friend of mine had a double feature at his house featuring both this film and The Curse of Frankenstein (1972) and lo and behold, both of them are considerably worse than the film that is almost officially considered the worst film ever. I wonder if there is any film in the world worse than these two!
http://www.imdb.com/mymovies/list?l=5184666