late 13c., from O.Fr. pissier "urinate" (12c.), from V.L. *pissiare, of imitative origin. As a pure intensifier (cf. piss-poor, piss-ugly, etc.) it dates from World War II. Pissed off "angry, fed up" is 1946, U.S. slang. To piss off "go away" is attested from 1958, chiefly British. Piss and vinegar first attested 1942. Piss-prophet "one who diagnosed diseases by inspection of urine" is attested from 1620s. Piss proud "erect upon awakening" is attested from 1796.