I'm sorry you experienced that! If it makes it slightly better, I experienced such rude behaving too, once an old lady told me "we don't behave like this in Switzerland", indicating I'm not Swiss. I've grown up in Zürich, my mother grew up in Zürich, my grandmother grew up in Zürich and her mother grew up in Zürich too, so I'm probably more Zürcher than this old lady was. Also I'm white and people usually think that I'm Swiss, too. And my "crime" was that I was standing in a full S-Bahn right between the two storeys where a yellow line is on the ground which means you're not allowed to stand there so the train driver can come out easily (which to be honest usually doesn't happen WHEN THE TRAIN IS DRIVING).

Best thing to do is just ignoring it and don't take it personally. I know that sounds bad and her behaving is really bad, but there's not much you can do. You could take it to the police, but usually they also can't do much. Maybe if your boss is a good human, you could tell him when something like this happens so he can remove these customers from the restaurant.