Green’s Dictionary of Slang

1. (Anglo-Irish) a British citizen who escaped to Ireland to avoid conscription in WWI .

1925

(con. WWI) Fraser & Gibbons Soldier and Sailor Words 96: fly boys: a name used contemptuously in Ireland for the English ‘refugees’ who crossed over to Ireland to avoid conscription.

2. (US) a pilot, civil or milit.; usu. with slight implication of disdain or dislike.

1946		J.W. Bishop ‘Amer. Army Speech’ in AS XXI:4 Dec. 248: Airforce flying personnel are sometimes labelled birdmen or flyboys.
1958		(con. 1950) E. Frankel Band of Brothers 226: And them flyboys figure they do the fightin’.
1966		W. Wilson LBJ Brigade (1967) 66: The flyboys’re apeshit. I know how their minds work.
1974		(con. 1940s) E. Thompson Tattoo (1977) 3: He measured his reflection in Kress’ plate glass against the image of soldier, sailor, flyboy and the occasional marine.
1987		(con. 1967) E. Spencer Welcome to Vietnam (1989) 107: On Main Street you see flyboys, Seabees, and sundry characters.
1996		(con. 1944) G. Pelecanos Big Blowdown (1999) 29: Movies set in the first war, dogfight movies mostly, smiling, long-scarved flyboys with Errol Flynn moustaches.
2006		F.X. Toole Pound for Pound 60: Trini loved the flyboys.
2012		C. Stella Rough Riders 57: I met him at a flyboy party [...] He’s here through the Air Force.