It's hard to decide which animated movies are the "greatest of all time", especially when you include both 2D and 3D features, but telling which ones are the worst is incredibly easy.
You just have to look for the animated films that are brazen ripoffs of good movies, unnecessary sequels nobody asked for or the ones that are simply too ugly to watch.
AlltimeMovies put together this list of 10 Worst Animated Movies Of All Time, and while I don't feel they all deserve the "worst of all time" title every film on the list is unwatchable, so "the worst" it is!