I am going to suggest that your moderators look over the rules again.
The user is clearly breaking the following rules. I have highlighted the rule they are breaking.
I. Inappropriate content will not be tolerated and will be deleted. This includes, but is not limited to:
Images, words, statements, username, signatures, or links that are, or refer to, sexual, drugs, vulgar, obscene, graphic, profane, defamatory, abusive, hateful, bigoted, violent, threatening, or otherwise offensive subject matter.
The following username is offensive, inappropriate, and hateful.
So if that is not good enough for you. According to,
http://dictionary.reference.com/browse/nigger"The term nigger is now probably the most offensive word in English. Its degree of offensiveness has increased markedly in recent years, although it has been used in a derogatory manner since at least the Revolutionary War. The senses labeled Extremely Disparaging and Offensive represent meanings that are deeply insulting and are used when the speaker deliberately wishes to cause great offense."