William Jayne Jacoby, known professionally as Billy Jayne and previously Billy Jacoby is an American actor, known for his roles in the teen comedy film Just One of the Guys (1985) and in the teen sitcom Parker Lewis Can't Lose (1990–1993). His siblings, Robert Jayne, Susan Jayne, Laura Jacoby, as well as his half-brother Scott Jacoby are also actors.

Just One of the Guys is a 1985 American teen comedy film directed by Lisa Gottlieb and co-written by Dennis Feldman and Jeff Franklin. It is a loose adaptation of William Shakespeare's Twelfth Night. The film stars Joyce Hyser, Clayton Rohner, Billy Jacoby, Toni Hudson, and William Zabka.