[Closed] Dealing with racism

I recently found out that someone I care about is quite seriously racist. I'm not going to give details, and I've tried having a light discussion about it, which resulted in them getting a bit mad and telling me I don't know what I'm talking about.

It's not a type of racism that will pop up a lot (probably never), but it still sort of bothers me. What's the best course of action? Or should I just do nothing?