The Rocky Horror Picture Show. I have seen it so many times I have lost count. I also got to see the "audience participation" version three times with my sister, but a group that is no longer together anymore (but I really wish they were still around) The Transducer Players.
The best shows were obviously the Halloween shows, which unfortunately I've only seen once.
The Rocky Horror Picture Show crowd has been my crowd since I was around 15. I don't like to be around uptight people when I'm trying to blow off some steam or have fun.