Monsters A-Go-Go was pretty terrible. Nothing happened, it was just people standing around talking most of the time, so there wasn't anything wonky or dumb or whatever going on to laugh at. The only real 'laughable' thing was the ending, but by then I had already attempted to kill myself several times.
Hamlet was another one in the same vein.
Movies like Manos and Hobgoblins are wacky enough that they are laughable even on their own, which is what makes riffing them so much fun.