Green’s Dictionary of Slang

(US) a scuffle, a skirmish; a beating.

1933		(con. WWI) F. Richards Old Soldiers Never Die (1964) 32: We had a brush-up with some German Uhlans.
1939		Pittsburgh Courier (PA) 1 July 11/1: You never did mention that early dawning brushing up Claudia Oliver got from one of the [...] tough boys .
1940		Raine & Niblo Fighting 69th [film script] Why? Because of that little brush-up? [HDAS].
1981		John ‘Piano ed’ Williams q. in McKee & Chisenhall Beale Black & Blue 137: [A] fellow stayed in his place, else them bouncers would carry him out of there and give him a good brushing up.

to thrash someone, to beat someone up.

1573

T. Tusser Five Hundred Pointes of Good Husbandrie (1878) 107: So Cisse that serues must marke this note, What fault deserves a brushed cote.

1. (US) to hit someone in the face.

1978

T. O’Brien Going After Cacciato 72: Next time the toad gets his fuckin’ teeth brushed.

2. (US gay) to perform fellatio.

1972		B. Rodgers Queens’ Vernacular.
1988		H. Max Gay (S)language.

3. (US black) to perform cunnilingus.

1980

E. Folb Runnin’ Down Some Lines 231: brush (one’s) teeth Engage in cunnilingus.

see under beaver n.¹

see under flat n.²

(N.Z.) a general admonition; don’t be a fool!

2003

McGill Reed Dict. of N.Z. Sl. 35: brush the teatree out of your hair Admonition not to be a dolt or to somebody who has made a doltish remark worthy of somebody residing amongst teatree or manuka in the backblocks. Mid C20.

(Aus.) think! use your intelligence!

1924

C.J. Dennis ‘’Ave a ’Eart!’ in Rose of Spadgers 88: ‘Time? Yes,’ I chips. ‘You’ll git that fer yer pains. Ar, brush yer brains!’.