j.b., n.² — Green’s Dictionary of Slang

j.b. n.²

also jaybee

[abbr. jet black; also a pun on j.c. or jaycee, a respectable, middle-class white person]

(US) a black person.

1946		Mezzrow & Wolfe Really the Blues 217: Man, you know one thing? This cat should of been born J. B.
1983		I.L. Allen Lang. of Ethnic Conflict 46: Color Allusions, Other than ‘Black’ and ‘Negro’: [...] jaybee [an initialism, j.b., for jet black].
2003		McGill Reed Dict. of N.Z. Sl. 116: jaybee A ship girl, from ‘jungle bunny’, Australian slang for a dark-skinned person.