Green’s Dictionary of Slang

1. a male homosexual; also as v., to sodomize.

1910		I.L. Pavia Jahrbuch für sexuelle Zwischenstufen No. 11 40: Zur Zeit des Prozesses O. Wilde (1895) und einige Zeit nachher wurde eine Homoseueller, ein ‘Oscar’ oder ‘Oscar Wilde,’ und das aktive Padizieren ‘to oscar’ genannt. Diese Ausdriicke sind leider noch nicht ausser Gebrauch gekommen [GS].
1938		Partridge DSUE (2nd edn) 1019/1: Oscar. A homosexual.
c.1940		Thomas & Davenport King’s Canary (1976) n.p.: Gahd! We’ll all get old if we stay here waiting for these two Oscars to crack an epigram.
1941		Baker Popular Dict. Aus. Sl.
1966		Trimble 5000 Adult Sex Words and Phrases.
1972		B. Rodgers Queens’ Vernacular.
2002		The-House-of-Love.org ‘Gay Men Names’ 🌐 Oscar.

2. (US) a stupid or unpleasant man; esp. when narrow-minded [? negative stereotype of sense 1].

1905		‘Hugh McHugh’ Get Next 77: Despair would grab him and he’d be oscar with the souse thing for sure.
1928		R. Fisher Walls Of Jericho 201: There now, you dumb Oscar.
1933		Ersine Und. and Prison Sl.
1946		Mezzrow & Wolfe Really the Blues 40: They were a hard lot of oscars in the Bridewell.
1958		‘Ed Lacy’ Room to Swing 40: Actually he’s a rough oscar and far from stupid—as a dick.

3. (US black) a man, irrespective of character.

1946

Mezzrow & Wolfe Really the Blues 50: Rapp was [...] the first oscar I ever heard who sounded a little like Bechet on the clarinet.