The Flintstones 6x20

Fred refuses to play the lead in the PTA show, ""Romeorock and Julietstone,"" opposite Wilma, so she casts Barney instead. Feigning the mumps, Barney (who is terrible in the part) drops out, forcing Fred to take over. But then laryngitis causes Wilma to drop out, so Barney rushes back in, now playing Julietstone!