There are some movies that are so bad they're entertaining to watch, and some are like torture. Manos is bad, but entertaining. So are movies like Plan 9 from Outer Space, Robot Monster, and Santa Claus Conquers The Martians. Then there are movies like The Trial of Billy Jack, which is like C-SPAN coverage of a Hippie Judiciary Committee meeting.
I'll agree with you on Plan 9, Robot Monster and Santa Clause Conquers the Martians but I couldn't even follow what was going on in Manos. Maybe I was too wasted but I think it was so bad that not even the MST3k guys could fix it.