It's got to be either Tank Girl or Frankenhooker for me.
It's easy to find BAD movies, but for "Best Worst", aka, "So Bad It's Good" category there should be some really redeeming qualities that make it interesting, entertaining, quotable, or just plain fun.
Tank Girl is a mess, with Ice (I'll do anything to be a movie star and get out of rap) T as a kangaroo-guy, early Naomi Watts as eye candy Jet Girl and smart-aleck Lori Petty leading the pack as Tank Girl. Weird as all hell but some absolutely hilarious dialog ("I had a swell time, but the swelling's gone down..") and it's fun to catch those building their acting careers - not just Ice T and Naomi, but Doug Jones, Iggy Pop, James Hong, Richard Schiff, etc..
Frankenhooker is possibly the better film but super-tongue-in-cheek fun, loaded with with it's-so-dumb-snort! dialog like "Errrrkkk! Hey - Wanna date?" and "Oh, God...She's gonna blow! Duck and cover!", of course plenty of 1980s bewbs for the less-discerning amongst us.
Both highly recommended...in fact, the higher you are, the better they are. ;)