I don't see how this can be a clearly defined rule without taking into consideration background, experience & both self-perception & how said individual is perceived. This idea of who can say "nikka" without it being inappropriate is something I have strong feelings about but I'm not sure exactly where I fall.
I do feel strongly that white people or anyone who identifies as being "white" should not be using it under any circumstance. However, a person with a white parent who identifies with being Black... I disagree that it should be so clear cut. If an individual, who is half white, but identifies with being Black & has had experiences, in this Country, that reflect how this Country treats Blacks...I don't feel that he should be looked down upon any more than any other Black person, for using the word.
Also, this conversation takes us into what it means to be Black in America or, more specifically, what does it mean to have the "Black Experience" in this Country.
Side Note: If you agree that no Black person should tolerate J. Cole saying nikka... should J. Cole's child be tolerated if the mother is Black?