I had a shituation like that once too. Customer came to my counter to complain about the treatment he got from one of my coworkers a few days earlier. I don't exactly remember what his real complaint was about, but throughout going on about "our new contrymen", so it made me wonder if his complaint was about the treatment, or about his golden brown skin and exotic accent. Told him to leave and not come back until he had fixed his attitude.
I was scared about how my boss would react when he would find out, but turned out he was totally cool with it.
If it weren't for some of these abusive people, retail work could be pretty enjoyable.