Jim is a slur used to describe Blacks in a derogatory way. Heard it used by Renko on Hill Street Blues. He called an older black man "Jim" and the guy flipped out and roared, "Who are you callin' Jim?" Most likely comes from the old Black slave character Jim in the book _Tom Sawyer_.
The word Jim is a racial slur that has been used historically to degrade and dehumanize blacks. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to blacks. If you are unsure about whether or not it is appropriate to use the word Jim, it is best to err on the side of caution and avoid using it in any situation.