Avatar the last air bender... They ruined the whole series with that movie... It is a mockery. And the twilight series, it is just pathetic. Also, if you ever get the chance, look up twilight parodies... They are hilarious!
A really difficult question, there is so much junk around. Italian SF movies from the 70s, german movies from the 50s and 60s, and some american monster movies from the 50s are certainly in the top 10.