The honor (or dishonor) of worst Mob movie goes to "The Valachi Papers" (starring Charles Bronson). The acting was terrible and it was almost funny to see all the "mistakes" shown in the movie (like 1960's cars in a scene that was supposed to take place in the 1920s).
This gets my vote, also.
The director had a great plot to work with, plus Bronson. But nope, it was a boring movie. I've seen nearly every mainstream mob movie more than once. But I can't bring myself to watch The Valachi Papers again.
