Green’s Dictionary of Slang

1. an effeminate-looking young man, though not necessarily a homosexual; also attrib.

1858		Era (London) 21 Nov. 11/1: Mr Webnaster and Madame Celeste represented the personages [...] Narcissus Prettyboy and Pamela.
1880		Aberdeen Jrnl 12 Apr. 2/6: Among her ‘mashes’ [...] is Gus Prettyboy, [...] an ulster, high-collared, square-top-hatted youth.
1885		implied in pretty-boy clip
1891		Aberdeen Jrnl 8 July 2/4: Mrs Hashley— You haven’t out a fire in Mr Prettyboy’s room [...] Mrs Tartly— I put a couple of mirrors in his room [...] He keeps himself warm by walking from one mirror to the other to look at himself.
1900		Bulletin (Sydney) 14 Jul. 24/4: ‘Quite so,’ said N.S.Wales’ Pretty Boy, with a twinkle in his eye, ‘the game was played once or twice before I left England.’.
1906		N.Y. Tribune 13 May 33/2: Was it not time that the pretty boy Alexis wore a star?
1916		Day Book (Chicago) 22 May n.p.: ‘Pretty’ Boy on Trial for Murder! - Oryet is Girlish and Slight - but Calm!
1924		G. Henderson Keys to Crookdom 400: Candy kid. A lady’s man. A pretty boy.
1942		H. Miller Roofs of Paris (1983) 87: He turns out to want a pretty boy instead of her!
1947		Essex Newsman 10 June 2/3: He feels he is getting away from his ‘pretty-boy’ tag and heading for some comedy and dramatic roles.
1959		G. Slatter Gun in My Hand 197: Didn’t think you’d notice. Too busy with your pretty-boy cobber.
1967		J. Rechy Numbers (1968) 16: A slight crook in his nose keeps him from being a prettyboy.
1976		N. Thornburg Cutter and Bone (2001) 87: He wasn’t, you know, what you’d call pretty-boy handsome. But he was good looking, all right.
1989		Beano Comic Library No. 182 22: Who’s your tailor, pretty boy?
1994		R.P. McNamara Times Square Hustler 41: Pretty Boy Tony is a young African American.
2001		G. Pelecanos Right As Rain 45: He wasn’t too good-looking so anyone would mistake him for a pretty boy.

2. (S.Afr.) a criminal who uses violence.

1963

L.F. Freed Crime in S. Afr. 107: A ‘goon’, ‘strong-arm man’, or ‘pretty boy’ is a criminal who employs violence.