SP, perhaps not, but perhaps they don't do it often because it simply has no effect - and that's the crux of the matter. The point is, when a white man calls a black man a "f***in black c**t", that's insulting, but not because the word 'black' is included. However, instead of taking offence at the profanities, which amount to the real insult, the black man ignores those and cries 'racist' because the only bit he really objects to is the word 'black'. Why? Why do you take exception to being told you're black? Think about it. Is that really an insult? I sincerely hope you don't see it as such, because by claiming it is, which is what you do every time you take offence at the word, you're agreeing with the racist that it is an insult, and therefore you're undermining yourself and every other black person in this world - which means you're giving the racist exactly what he wants, and so he continues. Why can't black people understand that? This really frustrates me.
Racists, like bullies of every description, thrive on reaction, so don't give them the upper hand by reacting as they intend, and expect, you to. If the word 'black' falls on deaf ears, the racist is defeated. Take a leaf out of Rosa Parks book and basically say 'Yes, I'm black. Now what have you got to say?'