Why do (uncivilized) black people call themselves n******, but then get mad if other people call them n*******?

I have often wondered the same thing i guess its just a personal choice of theirs to behave that way but also they are brought up in such family/broken environments that they behave like that, isnt it similar to if a person keeps calling themselves fat and that they need to loose weight etc etc but when someone else calls them fat they are hurt by it.