Green’s Dictionary of Slang

1. (US Und.) a novice thief.

1933		Ersine Und. and Prison Sl.
1949		Monteleone Criminal Sl. (rev. edn).

2. (US) an innocently honest person; a naive and foolish person.

1952		(con. 1948) G. Mandel Flee the Angry Strangers 426: You’re nervous, don’t kid me. Joe, you’re an old choirboy. [Ibid.] 439: [She] laughed at Joe himself, the worried choirboy waiting in the rain for her.
1955		P. Rabe Benny Muscles In (2004) 247: How would you know, choir boy?
1977		J. Sayles Union Dues (1978) 165: He’s a fuckin choirboy, Mitch, he don’t want any part of it.
1989		L. Roberts Full Cleveland 124: A guy fixes your car good, do you really give a damn whether he’s a choirboy? [HDAS].
2014		D.B. Flowers Bangs 246: ‘[Barrett] was no choir boy, but he was never violent’.

3. (S.Afr.) an accomplice, a young man who plays a supporting role in a crime.

1963

L.F. Freed Crime in S. Afr. 107: A ‘ringer’, ‘stooge’ or ‘choir boy’ is an accomplice.

4. (US gay) a novice male streetwalker.

1972

B. Rodgers Queens’ Vernacular 111: While starting on the beat [game, turf, walk] the inexperienced, up-and-coming choirboys, cowboys [...] wait to be approached.

5. (US) a novice police officer.

1975		J. Wambaugh [bk title] Choirboys.
1989		J. Morton Lowspeak 38: Choirboys – rookie, i.e. newly recruited policemen.

6. (US black) a derog. term for a black person seen as embracing white values.

1994

N. McCall Makes Me Wanna Holler (1995) 281: I was a choirboy, one of those trained, assimilated Negroes white folks love so much.

7. (N.Z. prison) an informer.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 42/1: choirboy n. an informer, a nark.

8. (S.Afr. gay) a homosexual male; thus in the choir adj., homosexual.

2003

K. Cage Gayle.