Green’s Dictionary of Slang

1. anything severely challenging, esp. in a ‘masculine’ context; a tough, masculine person; also attrib.

1977

D. Powis Signs of Crime 175: Brass balls – Something severe or testing, ‘a brass balls job’, or someone tough and unyieldingly masculine.

2. courage, ‘guts’; thus brass-balled adj., courageous, tough.

1960		in E. Cray Erotic Muse (1992) 329: If I had two balls of brass, and a john of a telephone pole, / I’d hie me to the northland, and breed with mare and foal.
1968		K. Brasselle Cannibals 39: This is the greatest stand-up guy [...] This guy’s got big brass balls.
1975		E. Torres Carlito’s Way 49: [D]on’t let them get to your skull. You a natural-born hustler with iron balls .
1982		(con. 1970) J.M. Del Vecchio 13th Valley (1983) 271: Medevac pilots got big brass balls.
1990		(con. c.1970) G. Hasford Phantom Blooper 38: I feel proud to be attacked by these brass-balled little hardasses, and proud to be killing them.
1995		J. Stahl Permanent Midnight 226: Not out of some brass-balled, muy macho, criminal behavior.
1997		C. Hiaasen Lucky You 187: Steel balls. I give him that.
2013		E. Beetner ‘Going in Style’ in ThugLit Feb. [ebook] [S]he broke horses for a living, a profession that gave her [...] ‘Brass balls bigger than both you boys’.
2020		S.A. Crosby Blacktop Wasteland 186: ‘Who came up with driving off the damn overpass? That was some brass balls shit there, I tell ya’.
2021		S.A. Crosby Razorblade Tears 236: ‘They must clank when you walk [...] Your brass balls’.

3. cheek, effrontery.

1976		P. Conroy Great Santini (1977) 233: I want to know which one of you worthless nits had the brass balls to cough when I was talking.
1995		C. Hiaasen Stormy Weather 46: They guy’s either incredibly stupid, or he’s got brass balls.
2004		C. Hiaasen Skinny Dip 214: I think you got some brass balls, considerin’ you’re the one got us into this train wreck.
2009		D.S. Mitchell Geezer Girls 4: If that bastard has the brass balls to gatecrach my wedding . . .