Green’s Dictionary of Slang

1. (US) a man, esp. a rustic, a peasant.

1894		‘Sl. of the Circus Man’ in Boston Daily Globe 17 Dec. 35: A countryman is either a ‘Rube’ (Reuben) or a ‘Jasper.’.
1914		B.M. Bower Flying U Ranch 174: Some uh boys help me rope him — like him and that other jasper over there done to Andy [DA].
1928		(con. 1918) L. Nason Top Kick 10: Them sheep-herdin’ jaspers they call reserve officers.
1931		‘Stampede’ in T. Goodstone Pulps (1970) 86/1: The first of these lost jaspers is Leonard Olsen.
1940		O. Strange Sudden Takes the Trail 18: How much did you take away from that jasper?
1952		Lait & Mortimer USA Confidential 86: Whereas all the jaspers in the Midwest look like Truman, who is their reflection, and are grinning gladhanders, most New Englanders look like Cal Coolidge.
1970		E. Thompson Garden of Sand (1981) 88: I don’t like this jasper.
1979		(con. late 19C) J.T. Edson Gentle Giant 56: I don’t know nothing about that jasper with the beard.
1989		H. Rawson Dict. of Invective (1991) 192: As for country dwellers, in addition to hick, names and nicknames that have been used disaparagingly as generics include: [...] jasper.

2. (US) a black person.

1912		A. Berkman Prison Memoirs of an Anarchist (1926) 248: ‘Hey, Jasper!’ the guard calls. The colored trusty scampers up the stairs.
1928		R. Fisher Walls Of Jericho 49: That jasper’s got mo’ bucks ’n you got freckles.
1929		T. Gordon Born to Be (1975) 236: Zigaboo, Dinge, Jasper; Nicknames for Ethiopians.
1986		L. Heinemann Paco’s Story (1987) 80: This Jasper — name of Rufus or Zebedee or Snowflake, or some lame-brained affair as that — must have been a busboy.

3. (US) the penis.

1955

in Randolph & Legman Ozark Folksongs and Folklore (1992) II 628: In shot old Jasper, Lucy got it all, / Lucy got a baby, after the ball.

4. (US prison/black) a lesbian.

a.1954		‘Ball of the Freaks’ in D. Wepman et al. Life (1976) 110: There was a jasper named Nora and a bitch named Dora.
a.1962		‘Konky Mohair’ in D. Wepman et al. Life (1976) 107: A fine young jasper with sixty-inch thighs / And tits squirting sweet muscatel.
1971		S. Stevens Way Uptown in Another World 219: She’s a jasper, you dig? I met her in Kansas City and she hadda get tied to stay outta jail on a lesbo charge.
1977		(con. 1960s) D. Goines Black Gangster (1991) 133: Dot is colder than any damn jasper.
1980		E. Folb Runnin’ Down Some Lines 159: There are several vernacular expressions for a lesbian: [...] jasper, lesbie, butch.