Subculturally correct. Comes from the Merry Pranksters: Ken Kesey said "you're either on the bus or off the bus", a "get with the program" hint to Sandy Lehmann-Haupt. At best, it refers to someone who Gets It, somehow passing the vague criteria to be a member of the tribe. Is it Hesse or Huxley this week? Am I weird enough? Secret handshake? More recently, with "hipness" a mass-marketed commodity, it applies to fringe sheeple who sneer at mainstream sheeple.