brass neck, n. — Green’s Dictionary of Slang

brass neck n.

[the toughness of SE brass + neck, i.e. able to stick one’s neck out under neck n. without risk of hurting it because it’s made of brass; but note brass n.¹ (2) + neck n. (3a)]

1. impudence, audacity; often in phr. have a brass neck.

1938		Dundee Eve. Teleg. 21 Mar. 6/2: Some people would say it was ‘brass neck’ on behalf of the motorists.
1953		Aberdeen Eve. Exp. 14 Mar. 4/2: The root [of the problem] is a combination of conceit and complete brass neck.
1966		P. Boyle At Night All Cats Are Grey 68: Apparently the bloody cut-throat had the brass neck to call to see Kreuger the next day.
1969		P. Boyle All Looks Yellow to the Jaundiced Eye 56: For sheer brass neck and general effrontery, you must hand it to the little weasel.
1986		F. Taylor Auf Wiedersehen Pet Two 255: How they’ve got the brass neck to turn up here, I don’t know.
1999		Indep. Rev. 30 June 4: An MEP [...] has the brass neck to try and snatch the presidency.
2006		A. McCall Smith Right Attitude to Rain (2007) 145: Isobel tried to imagine what it would be like [...] to have the brass neck to nose round other people’s houses.
2017		V. McDermid Insidious Intent (2018) 100: She didn’t think he’d have the brass neck to show up.

2. an impudent, audacious individual.

1993

S. Armitage ‘People talk nonsense...’ in Book of Matches 9: Call me brassneck, call me hard-faced.