I'm gonna ditto Xeno with Feast being way up there. It's amazing how good the first of a series can be while the rest is pure garbage, feast being one of the greatest examples of how bad a movie can get, each generation.
I'm a bit of a bad movie snob. I love B movies and worse, as long as there is something for you to latch on to. Was really bummed when the Chiller channel went dark but it doesn't keep me from surfing for bad movies to watch and re-watch.
With that said, my contribution is Dirty Mary, Crazy Larry. It's the movie that made me fall in love with Chargers at 8 years old.
I'm surprised "The Room" hasn't been mentioned? Absolutely terrible, but funny in an unintended way. If you haven't seen "The Disaster Artist" Go see it. "Riff Traxx" of the original "The Room" is hilarious!
Mortal Kombat: Annihilation is my second favourite film ever; I quote it almost daily and replay scenes in my head daily as well (ha[[ens with a lot of movies/songs).