IMO 3 types of movies are not worth watching
1) Pre 1990
Exceptions being The godfather (only first part) and 2001. 2001 can bore people to death but it is only worth watching because it has deeper meaning. All other pre 1990 movies are too slow to enjoy by modern viewers.
2) With sub 7.0 rating on IMDB
This is not a cliche. I have found the IMDB 7.0 rating barrier to be VERY accurate. Any movie rated below 7.0 is weak or plain bad. But IMDB rating should only be used for filtering out bad movies, it does not accurately represent good movies. There are many average movies are are rated highly on IMDB (e.g., inception, the dark knight etc).
3) All david fincher movies
Exception, Mulholland drive