Green’s Dictionary of Slang

1. a dull, stupid person, a pest.

1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 257: jeff (n.): a pest, a bore, an icky.
1944		in ‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.

2. (US black) a derog. term for a white rustic, a peasant, esp. a Southerner.

1946		Mezzrow & Wolfe Really the Blues 307: Jeff Davis: an unenlightened person, a hick from down south, sometimes shortened to jeff.
1961		R. Russell Sound 144: Them Jeffs is workin’ together!

3. an admirable person.

1953

L. Durst Jives of Dr. Hepcat (1989) 5: All the cats conjugate to elucidate, the Jims, the Jeffs and the Joes. [Ibid.] 8: Don’t be a square and act like a bear get with the jeffs that’s going somewhere.

4. a white person, esp. if a racist.

1958		C. Himes Real Cool Killers (1969) 107: Shhhh [...] Chalk the walking Jeffs.
1964		R.S. Gold Jazz Lex. 165: Jeff, n. [...] A white person, but esp. one who is hostile to negroes.

5. a black person who is obsequious towards whites.

1969

PADS 51.29: Names [for a black man who is subservient toward whites] used exclusively by Negroes...jeff, jeffer, jeff davis, jeff artist [DARE].