Green’s Dictionary of Slang

1. (also beeby) a police officer, a police car.

1883		J. Greenwood Odd People in Odd Places 68: The instrumental ‘blue boys’ belonging to several metropolitan divisions.
1908		N.Y. Eve. Journal 18 Sept. in Fleming Unforgettable Season (1981) 227: John T. Brush handed Brother Bingham a line of conversation regarding the necessity of policing the grounds [...] and he will send a couple of hundred blue-boys to hang around and make themselves useful.
1909		‘The Lang. of Crooks’ in Wash. Post 20 June 4/1: [paraphrasing J. Sullivan] The policeman is [...] a bull, a beeby, a fatty finger or a harness bull.
1915		‘Doss Chiderdoss’ ‘Lady Friends’ Sporting Times 13 Mar. 1/2: It is true they are in service, but a cook I always greet / As a lady, and as gentlemen the cooks our blue-boys treat.
1933		M. Marshall Tramp-Royal on the Toby 120: ‘You can arrest me when I come back, can’t you officer?’ Boy Blue pondered deeply.
1942		Berrey & Van den Bark Amer. Thes. Sl.
1949		Monteleone Criminal Sl. (rev. edn).
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 395: Nicknames current among boys [...] include: Bobby, Blueboy, Boy in Blue.
1966		M. Rumaker Exit 3 and Other Stories 109: Watch it, blueboy. You coppers think you can get everything for nothing.
1975		L. Dills CB Slanguage 14: Blue Boys: local police.
1980		E. Folb Runnin’ Down Some Lines 66: The police are characterized in terms of the uniforms and the colors that mark them as the legal arm of the establishment (blue coats, blue boys, little boy blue).
1984		Smiley Culture ‘Cockney Translation’ 🎵 What cockney call a Jack’s we call a Blue Bwoy.
1995		J. Cameron Vinnie Got Blown Away 29: And guess what, there was two blue boys in 141.
2001		‘John le Carré’ Constant Gardener 501: When did you ever put on your best suit, trolley round to the Blue Boys’ headquarters [...] ?
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 21/2: blue boy n. a policeman.

2. (US prison) a warder.

1963

in T.I. Rubin Sweet Daddy 37: Some of these blue boys real twists.

3. (drugs) amphetamine.

2001

ONDCP Street Terms 3: Blue boy — Amphetamine.