The Barbershop Quartet is a group of four men, who sing upbeat vaudeville style songs, generally about rather indecent topics, such as AIDS, vasectomies, and abortions.
In "The Cleveland Loretta Quagmire", a cutaway shows Peter working as a doctor, accompanied by the Barbershop Quartet. He and the quartet come in and sing to a man that he has AIDS, in the song "You Have AIDS".
In "Mo' Jobs", The Barbershop Quarter appears again to show Peter the ropes of working as a
In "New Star Stew-Dent",
In "Partial Terms of Endearment", they sing to Lois, explaining the process of abortions to her.
In "Holly Jolly Folly", they sang Christmas songs.