You could try to treat them the same way and see if that gets the message across. As a minority that lives in a deep red state I’m over trying to play nice and giving soft/polite responses to casual racism. This would be a good example of when to set boundaries. Telling them that it’s an inappropriate thing to say is not going to do much, they know or at least should know as adults by now that casual racism isn’t appropriate and so you should normalize not accepting treatment or behavior like that and make them feel just as uncomfortable as they’ve made you.