Green’s Dictionary of Slang

boys in blue n.

also bellies in blue, blokes in blue, boys blue, gentlemen in blue, men in blue
[note 1920s UK boys in blue, permanently disabled ex-servicemen, some 7000 of whom were inmates of hospitals in Greater London area and wore a blue uniform; early use meant the Royal Navy; bloke n. (3)]

1. the police; occas. in sing.

[Aus]Bell’s Life in Sydney 8 Apr. 3/1: I will take Srah to the stronghold of the men in blue who protect the people.
[UK]Paisley Herald 6 Feb. 2/3: The ‘men in blue’ had to be called in to put down the ‘ghosts in white’.
[UK]Sheffield Eve. Teleg. 19 Aug. 2/5: The Boys in Blue. The London policeman so often is the mark for criticism, for censure and for ridicule.
[Aus]Dead Bird (Sydney) 9 Nov. 2/3: Upon going to his house a well-known gentleman in blue found nailed upon the door a placard running thus [etc].
[UK]Sporting Times 11 Jan. 1: Certain it is that our merry boys blue are no mean elocutionists or chirrupers.
[UK]J. Astley Fifty Years (2nd edn) II 235: [...] subsequently retiring, leaving the boy in blue to keep watch.
[UK]C. Scott ‘The Lay of the Man in Blue! Gallant Rescue by a Policeman’ The New Victoria Cross 6: Dead! to save God’s saddest creatures! Faithful Man in Blue!
[Aus]Truth (Sydney) 14 Oct. 7/4: The pickpocket gambles, the forger, too, / [...] / For each takes chances the ‘boys in blue’ / May surprise him in his sin.
[UK]Albert Chevalier ‘The Racecourse Sharper’ [lyrics] You must dodge the bloke in blue unless you wants a week in quod.
[UK]E.W. Rogers [perf. Vesta Tilley] The New Policeman [lyrics] I’m the new policeman, I'm the dandy boy in blue.
[Aus]Bulletin (Sydney) 17 Nov. 12/2: Glittering buckles and eccentric flop-hat added snap to a toilette which achieved the unique feat of dazzling a policeman. The ‘bhoy [sic] in blue’ must be pretty tough, but this particular one seemed knocked all of a heap.
[UK]Sporting Times 6 Jan. 8/3: [advert] The Lads in Red and The Boys in Blue smoke Old Gold Cigarettes – Of course You do.
Laverton Mercury (Laverton, WA) 15 Jan. 3/3: That the ‘man in blue’ asserted his authority and closed both hotels up early in the evening - one much earlier than the other.
[UK]Wodehouse Psmith in the City (1993) 88: ‘You ’op it,’ concluded the man in blue. ‘That’s what you do. You ’op it.’.
[Aus]Truth (Sydney) 10 Nov. 12/2: [headline] LIZZIE LUMBERED. A Sussex Street Solicitress BUMPS A BRACE OF BOYS IN BLUE.
[UK]‘Doss Chiderdoss’ ‘Lady Friends’ Sporting Times 13 Mar. 1/2: He spoke up for the man in blue in court the other week.
[UK]Dover Exp. 27 Mar. 15/4: The Boys in Blue from the great ‘Metrollopus’ came down here and they didn’t half wallop us!
[UK]Buckingham Advertiser 18 June 4/3: The boys in blue once again proving what excellent cricketers and what jolly companions the Police Force can be.
[US]R. Chandler High Window 157: You got back on at six. Shortly after that the boys in blue came bustlin’ in.
[Aus]Truth (Sydney) 24 Jul. 12/1: [S]oon after the fire broke out someone whispered in the ears of the boys in blue, who were quickly on the scene and made four arrests.
[US]N. Algren Walk on the Wild Side 243: The parlor was full of the boys in blue and someone smashed the glass of the juke.
[UK]I. & P. Opie Lore and Lang. of Schoolchildren (1977) 395: Nicknames current among boys [...] include: Bobby, Blueboy, Boy in Blue.
[US]J.P. Donleavy Fairy Tales of N.Y. IV i: Policemen were parked sitting in their car, in their nice blue uniforms waiting for speeders [...] Ha, ha, you’ve never seen such bellies in blue.
[Ire](con. 1890–1910) ‘Flann O’Brien’ Hard Life (1962) 111: Jesuits can be a far closer police force than the men in blue.
[US]B. Jackson Get Your Ass in the Water (1974) 93: Up come the boys in blue, cuts your head something terrible, and carries you to jail.
[Aus]D. Ireland Glass Canoe (1982) 5: Not that the boys in blue were waiting outside the pub to put the bag on departing drinkers.
[UK]Flame : a Life on the Game 138: I was fast asleep when the Boys in Blue raided Betty’s.
[Aus]C. Bowles G’DAY 25: A pig is one of the boys in blue and busts you for speeding.
[US]R. Shell Iced 262: They called the police. The men in blue arrived and found me raving.
[US]Ian Dury ‘Itinerant Child’ [lyrics] Slow down itinerant child, the boys in blue are waiting.
[UK]N. Barlay Hooky Gear 230: Once youre inside, and bunkbedded, and spanking the old monkey, I will personally let it be known what a tremendous help youve been to the men in blue.
[UK]Jin ‘Club Song’ [lyrics] Keep away from the boys in blue.
[US]F.X. Toole Pound for Pound 77: The men in blue were on his side.
[UK]D.S. Mitchell Killer Tune (2008) 84: They boys in blue were trying to swap the beat of the street for some other type of melody.
[UK]K. Sampson Killing Pool 172: He’s had a bad deal from the boys in blue, especially in aftermath of the riots.

2. baseball umpires.

[US]M. Avallone ‘Power the Ball Platewards’ in Super Sports [Internet] Most of the boys in blue brush off home [plate] after a terrific slide.

3. (US prison) warders.

[US] in T.I. Rubin Sweet Daddy 37: Hacks, screws [...] they’re still boys in blue to me.