RPHS is a "rock n' roll" peice of interractive theatre... and it helps that it has an absolute KILLER soundtrack. The movie absolutely bombed when it was first released. It didn't find it's audiance until the "midnight movie" craze of the late 70's and early 80's.
A lot of really cool movies became midnight cult fodder: Ralph Bakshi's Wizards, A lot of John Water's early films, Plan 9 From Outer Space, Dark Star, Fantastic Planet, Forbidden Zone, among many, many others....
But Rocky had the advantage: It was a musical that you could get up and dance to... AND it encouraged the audiance to let their weirder natures out... cross dressing, bisexuality, and a generally accepting atmosphere was fostered in those audinaces. (which is why the pafter parties were so addictive... I got a LOT of action at those passion pits! At times, it was like being in the movie "Short Bus" LOL)
Rocky is a great "DB" filter, to this very day... Take someone to Rocky, and see how they react. If they get into the audiance participation, they're probably pretty cool. If they just sit there an ***** about how these people are spoiling the flick... well, there you have it: they're a DB.
Number Two: Conform, Number Six! Conform!
Number Six: I will not be stamped, filed, indexed, briefed, debriefed, or numbered! I am a person.