My conversation would have gone more like this.

Me: Ma’am, you forgot the rest of your change.

Tourist: Oh! I guess I did, unless you were paying me in pesos.

Me: Excuse me?

Tourist: Pesos. The money in Mexico.

Me: Yes, I know what a peso is. But we're not in Mexico, so you're welcome. Unless you meant to overpay.

Tourist: No, I was referring to the fact that you're Mexican.

Me: No.

Tourist: Puerto Rican?

Me: Are you Irish?

Tourist: Cuban?

Me: Polish?

Tourist: What?

Me: Aren't we playing a game? You guess me, I guess you? What do I get if I win?

Tourist: You're being disrespectful. Where's your manager?

Me: Shall I call her? Because I've said nothing any more disrespectful than you have.

Tourist: Well, I never.

Me: Unfortunately, I do every day. Here's your change. Have a nice day.

Assfart.