The Apple
This first time I saw this was at an after hours movie club we had at one of the theaters I worked at. One of the bartenders there ran a local psychotronic movie group and had a very esoteric knowledge of cult movies. He always raved about this one and was so excited to show it for movie night (he also brought barbeque from the other bar he worked at). 900
It was a huge hit.
The costumes and set design in this is are astounding. The relentless pummeling ridiculous music numbers somehow doesn't get overbearing because each one is so absurd in its own way. The wild dances help too. My only minor issue with this is the abrupt, left turn ending that is so overt and ludicrous it somehow jars you from what is already a ludicrous movie.
In a just world this would be getting the same level of fandom as something like Rocky Horror. 596