Earlier quoted context omitted.
Obviously not the same but I've had this happen in a couple places and I just say "FUCK OFF" as loud as I can and get visibly upset and they leave me alone after that.
....That's a horrible way to react. I wonder what these people think about you and your country of origin. You are, after all, an ambassador for your country when ever you are outside it.
> I wonder what these people think about you
If they're acting at all as GP described, then it's obvious they see you as another mark to aggressively try to extract money from.
Caring about what some bothersome strangers think about you and where you're from takes a distant backseat to standing up to aggression.