Green’s Dictionary of Slang

1. (US black) a rustic, a peasant, usu. from the South.

1942		Berrey & Van den Bark Amer. Thes. Sl. §391.3: rustic, bumpkin, Jeff Davis, jeff, a Southern ‘hick’.
1946		Mezzrow & Wolfe Really the Blues 218: He’s a Jeff Davis from downunder and ain’t been up here a hot minute.
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: [...] Jeff Davis (a Southern hick).

2. (US black) a black person who behaves subserviently 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].