Shortened slang term of 'white nigger'. Basically meaning that the subject, although white in skin, is black in personality.
This causes endless frustration across the social spectrum since the common belief of most people is that surface details rule all and heaven help anyone who attempts to live up to stereotypes other than their own.
In truth, it only leads to more hypocrisy. You can wince when you see black guys complaining about white guys rapping but some people remember the prejudice Living Color and Body Count faced when they tried stepping on 'white' musical territory and doing rock and stroke or metal.
Fighting fire with fire is probably the least effective way of dealing with racism.