Green’s Dictionary of Slang

irritated, fed up, annoyed.

1940		Blyth News 27 May 3/1: Brassed off signifies that the speaker is feeling fed up or suffering from ennui.
1940		C. Gardner AASF 189: Cobber said he was ‘brassed-off,’ especially after he had got half - way home once, only to be called back to hand over his flight and teach two new-comers the way around.
1945		‘Evacuation Song’ in Mess Songs & Rhymes of the RAAF 19: They’re shit-scared and frightened, and brassed off as well.
1946		G. Gibson Enemy Coast Ahead (1955) 28: We had waited so long that we were all completely brassed off.
1958		(con. 1940s) B. Behan Borstal Boy 216: We would not be long getting brassed off with it.
1961		B. Crump Hang On a Minute, Mate (1963) 68: The hospital people at Kaitaia were getting a bit brassed off with Tonker.
1977		(con. 1940s) S. McAughtry Sinking of the Kenbane Head 106: I was pretty brassed off with Jake Thomson.
1982		L. Cody Bad Company 82: She might be brassed off enough to talk to you.
1996		(con. 1970) G. Moxley Danti-Dan in McGuinness Dazzling Dark (1996) II iii: I’m brassed off with fellas, full stop.
1999		J. Cameron Brown Bread in Wengen [ebook] ‘[T]hey get a bit brassed off with you only talking to George Marshall’.