What's your favorite SO BAD IT'S GOOD movie?

You know what I mean; a movie so brainless, cheesy or inept that no one should like it but it's just so great because it's just so bad.

Movies like Plan 9 from Outer Space, Manos, the Hands of Fate, Birdemic, and The Room are staples of the genre but there's so many others to consider.

For me, it's the much maligned Battlefield Earth. It's a masterclass in how NOT to make a $75,000,000 Hollywood popcorn epic. You can almost feel your braincells dying as you view it. The acting is terrible, the effects look like something created in MS Paint, it's stupidly directed, the script is inexplicable, and it's visually ugly but it's also very entertaining for all those same reasons.

Yours and why?