I've seen it four times.
The First Time I Saw "The Rocky Horror Picture Show": I was a freshman in college, and the university activities board put on a midnight showing. A friend of mine and I drank a bottle of Seagrams before we went. We weren't willing to dress up in the silly costumes, but someone told us it was okay if we wore trenchcoats, so we did.
Anyway, the movie was shown in the big ballroom in the campus union building, and they covered the floor and the walls with butcher paper, thinking that would be enough. The FOOLS! We did a little movie-watching, a little water-squirting, a little toast-throwing (best moment: tossing a slice of wet toast in the air and hearing someone yell, "EWWWWW!" when it hit them), and quite a bit of chair-throwing and borderline rioting. It was fun!
The Second Time I Saw "The Rocky Horror Picture Show": Two years later, the activities board finally screwed up their courage to try again. This time, they got smart and showed the movie outdoors. The same friend and I got together, drank another bottle of Seagrams, and wore the same trenchcoats. This showing was much more sedate, though I looked for excuses to throw chairs. They also found a bunch of Rocky Horror fanatics who knew all the audience participation lines, and they helped everyone get into the spirit.
The Third Time I Saw "The Rocky Horror Picture Show": It was at a friend's house. "Rocky Horror" had just been released on video. I was the only person who had ever seen the movie. They wouldn't let me throw chairs. They also wouldn't let me holler any of the lines ("Quiet! We're trying to watch the movie!"), (then they complained afterwards: "That wasn't so good -- what was the big deal?") so it was kind of a waste.
The Fourth Time I Saw "The Rocky Horror Picture Show": At a completely different college and, unbelievably, even lamer than watching it on video. We showed up ready to do battle, and they told us we weren't allowed to bring water guns or toast into the theater. Wha? "Somebody might try to sneak a real gun in there." Hey, sister, does this ORANGE PLASTIC SPACE GUN look like a FUCKING UZI to you?!? Well, we had to leave our water guns at the desk, but our toast was safely hidden in the inside pockets of our jackets, so they didn't get that, ha ha. They also had campus cops patrolling the theater. Unbelievably pointless.
Okay, who's next?