Green’s Dictionary of Slang

brat n.¹

(US prison) the young partner of a prison homosexual.

1931–4		D. Clemmer Prison Community (1940) 330/2: brat, n. A boy used for sex purposes, a ‘punk.’.
1944		O. Ferguson ‘Vocab. for Lakes, [etc.]’ AS XIX:2 104: A boy who presents himself to the uses of buggery is a punk (common) or a brat (more special).
1953		T. Runyon In For Life 99: I’ve seen the patient papas carrying sacks of canteen stuff for their boys — also known as bronchos, gunsels, kazoonies, kids, brats, and, mostly, punks.
1962		Ragen & Finston World’s Toughest Prison 792: brat – A passive sex pervert.
1972		B. Rodgers Queens’ Vernacular.
1992		Bentley & Corbett Prison Sl. 58: Chicken A young, pretty homosexual. Although any young, pretty homosexual is considered a chicken, it is used more often in reference to blond ones. (Archaic: brat).

SE in slang uses

In compounds

brat-getter (n.)

the penis.

1890–1904

Farmer & Henley Sl. and Its Analogues.

brat-getting place (n.)

the vagina.

1890–1904

Farmer & Henley Sl. and Its Analogues.