http://en.wikipedia.org/wiki/The_Rocky_Horror_Picture_Show_cult_following said:
There are many aspects and levels to participating at a showing of this movie. Many people just yell at the screen while others go much deeper. Many people develop over time into die hard fans. During the song "Time Warp" in many theatres nearly everyone stands up and does the dance. Costumes, props, and verbal dialogue are all tools in participating.
Typically, a showing that uses a shadow cast will include a pre-show ritual that involves calling attention to anyone who hasn't seen the film in a theater. Those who haven't experienced Rocky Horror "live" are considered "Virgins". Depending on the theater and shadow cast, Virgins will be called out, mocked, made fun of (usually in a good-natured-but-vulgar way) and encouraged to participate in party tricks and games that might be considered racy or demeaning. It is not uncommon to have rubber balloons (or even inflated condoms) placed between a "virgin's" knees to be popped by cast members. In the 1990s, casts in New York and Virginia would fill a "Virgin's" mouth with whip cream and put a cherry on top, etc. A Nashville-based pre-show includes parading the "Virgins" up and down the aisles of the theater with balloons (referred to as "cherries") held between their knees, while the song The Ecstasy Of Gold from the soundtrack to The Good, The Bad & The Ugly plays throughout the house.
Although the levels and intensity of the preshow hazing varies from cinema to cinema, it is considered to be "in good fun" and rarely pornographic or dangerous.