AITA for cancelling my week long visit with my SIL after she made a racist remark about my brother's biracial girlfriend?

I had plans with my wife to visit her family for a week, SIL and her husband are the only ones left in the town where my wife grew up, BIL always tagged along on our visits there until he graduated college and moved to a different state for work.<br><br>My wife and I decided it would be a good time to visit as my son had spring break and my daughters quarentine ended after returning from college so we could all spend time together with her family.<br><br>While I was setting up the boy's room, I overheard my SIL talking with my wife and she asked "How's your brother doing with his new bed slave?" I stopped what I was doing to listen and my wife giggled and replied "He's very happy, you know how he is, but I think they're serious about each other". I never heard either use that kind of language before but decided not to address it then and there.<br><br>We were all in the kitchen when my BIL called to check in, SIL started making small talk and brought her girlfriend up saying "How's his new bed slave?" To my surprise everyone laughed. After they stopped I told my SIL "I think it's about time we head back home, or you can take us to the airport". My wife started yelling at me and my daughter asked what was going on, I told her I was not going to let someone I had known her whole life call her a bed slave, my son then chimed in with "Yeah and she called Kailee a nigger" My daughter started yelling at her mother that she was never going to see her again.<br><br>So now my wife and her family think I'm the biggest asshole in the world, her father called me telling me that I ruined a family gathering over a joke that didn't even get said, and even some of my friends think I was being a little too sensitive.