Superfluous answer but since nobody's said it yet, Troll 2, the true Best Worst Movie.
My mates were interviewed for "Best Worst Movie" at a convention somewhere, and said the reason they were there was because I'd made them watch it so often. I've never seen the doc so I can't say if they made it to the final cut or not. Oh, and another mate was on tour with his band, needed some dental work and realised it was only 45 minutes out of his way to get the guy from Troll 2 to do it. Apparently, he was very happy to share stories and accept the adulation.
"The Room" is in one of my favourite sub-genres, the vanity project. Stuff like the aforementioned "Cool As Ice" and "Miami Connection", and:
Tiger ClawsJalal Merhi was a jewel salesman in Canada, but cashed out of the family business to get into movies. He's still working today, just about, but this is about him and Cynthia Rothrock as a couple of cops who are trying to take down a serial killer who's going after martial arts instructors. He's a decent martial artist but beyond terrible as an actor, and has negative chemistry with Rothrock, who tries gamely. There are lots of scenes where she's just sat in a car twiddling her thumbs while Jalal is kicking ass in a warehouse somewhere. The sequels are pathetic, too. Enjoy it on Youtube
here.
A few others that just popped into my head:
GigliPerhaps not as funny as its initial detractors would have you believe, it's worth watching because it feels completely unfinished - 90% of the movie takes place in an empty apartment or driving round in a car. You could tell me they'd released the rehearsal footage by accident and I'd totally believe you.
ThingsThe director once sent me an abuse-filled email because my payment for a copy of his DVD was three days late. His previously unreleased "Wicked World" was just released on blu-ray, but I've yet to pluck up the courage to watch it.