The comedy show at NYC's Supper Club features a rotating cast of up-and-coming comedians, scantily clad dancers, and hip-hop DJs, as well as racy audience-participation segments best left undescribed in a family magazine. WHO'S LAUGHING Relying strictly on word of mouth, the high-energy program, which has been running since April, plays to sold-out crowds every Saturday night and recently attracted Julia Stiles, Rose McGowan, and Jerry O'Connell. COMIC RELIEF ''I don't like the standard 'Hey, you ever notice when...?' type of comedian,'' says host/creator (and former Wall Streeter) Jeff Beacher. ''The comedy world is freaking out about [the show] because it treats comedy as it should be treated -- the comedians don't get paid, they just want to get on that stage, play off the energy of the 1,200 people there.''