I say its pretty easy to ignore the problem when you're not the target.
"Isms," degrade us all regardless of which ism it is.
To be perfectly honest, there's no unwritten rule that says you both can't have your beliefs and still work with one another.
He rented your ears for music and recording, not as a bully pulpit. If he was a record industry A lister and you were worried about being blacklisted then it might be a bigger issue. As it stands, you seem like a smart guy.
Redirect him back to the session when he gets back onto his bullshit. Dead serious. Be the adult.
Him: "Blacks are this, Polish are that, Jews are that etc..."
You: "Ok I've got the next track armed and we are all ready for you to punch in your verse."
Him: "But seriously you never had to deal with a lazy N****????"
You: "I'm pretty sure the mic's warmed up. I'm ready when you are."
Him: "What are you a n**&& lover?"
You: "Hey man, remember you said yesterday you really wanted to focus on your quadrilles, I'm just trying to get this song in the bag so we can move onto that and give it the time it deserves."
All of this in so many words equates to I don't really give a shit about you and your ideology
. I'm just here to work, that's what you're here for, lets get this over with
. You shut him down in the nicest way possible so that you don't have to choke slam the guy.
As far as ignoring it goes, its your asshole boss who I'd be watching like a hawk.
His (your bosses) advice to ignore it is founded on some level in a racist (subconscious) ideal. Its not like you're black so what's the problem? Think about how even thinking about it that way
is racist for a second and you'll see my point.
They must not be so passionate about racism or preventing it in their place of business....but discrimination often comes in threes, God forbid you are gay or have a gay relative, get into a relationship with a Black woman or a Latino or went to college. You two shall clash again, mark my words.