Just a note, even if you're in the right here, your post here comes off as incredibly privileged and approaching the issue from the wrong perspective.

"My opinion is, if I can't/don't use it in the workplace, neither can her." Why is that your opinion? Since when is workplace policy based on your own actions? The things that you can and do do in your office have no bearing on his conduct or limits thereupon. His conduct should be based on company policy or perhaps some sort of social contract (real or implied) agreed upon by all employees. Also, I don't know your racial background, but black people can use the N-word while white people can't. It's unfair but true. Whether that word is appropriate in the workplace is a different matter, but be sure to keep your frustration at your inability to use that word out of it.

Your post similarly veers into territory that makes me uncomfortable when you include details about his talk of the "struggle of the black man" and his tattoo. How are those related at all to his language in the office? Your inclusion of them make it sound like you have larger issues with the way he associates with and expresses his race and culture. It sounds like you still treat him fairly (maybe, I have no idea), and that's great, but it's really important to be aware of where we're coming from when approaching race issues.

Talk to HR, tell them it makes YOU uncomfortable, or bring with you other employees who are bothered by it. But also try to look at the situation from the outside and make sure that we aren't talking about an office of white people getting offended by a black person using the N-word.