Hey Bo. You know as well as I do that the whole "joking" excuse is total bullshit. I've heard plenty of racist jokes and even told a few. They usually start with "a black guy and a mexican walk into a bar" or something else that makes it obvious that a joke is about to be told. I even used to have an african guy that worked at my job. He was so ridiculously lazy! I said PLENTY about him like that when he stank up the bathroom it was probably because he ate lion asshole for dinner, lol. But guess what? I joked about that with the other two black guys that I worked with who also hated how lazy he was. They had their own jokes too. However when you start spouting off about a black woman who needs a kidney transplant being an incompetent n*gger, that is just ignorant and cowardly. If he truly thought that kind of speech was acceptable he'd speak that way in public and around his black/spanish/whatever friends. The fact that he saves such speech for when blacks or whomever else isn't around shows that he's a disgusting coward just like so many other racists.
I'm mixed and I had MANY negative dealing with black men in my past. That never drove me to start calling black people worthless n*ggers or anything as stupid as that. To be fair I don't like the stereotypical black man who has his pants hanging off his ass, refuses to speak proper english and is disrespectful to everyone beyond all belief. But guess what? There are also white men, asian men, and spanish men who are exactly the same. In general I realize that I don't like people, mainly because most people are arrogant and ignorant. Maybe your bf will realize one day that you can't single out one race to embody all of the negativity that he is trying to pin on them.
I don't think that you should just up and dump him over something like this like others have suggested. However you need to ask yourself if his refusal to change something as simple as his speech might be an indicator of how willing he is to change other more important attributes when your relationship is further down the road. You also need to ask yourself if his "joking" also might extend to women, and therefore you. We've already established that he is a coward and possibly a bigot, so who's to say that he doesn't talk about how "women are stupid and only good for sleeping with"? I'm sure his black friends aren't aware of his constant and belligerent use of "the -n- word", so maybe you aren't aware of the derogatory things that he says about women (or you personally).