Could have been brits/europeans/australians...
I see the server grimace when they hear our accents. I tip 20%.
However, I do argue blind with people from my country that tipping IS NOT OPTIONAL. And that THEY ARE IN ANOTHER COUNTRY. People who can afford it.
Might have become even worse for us brits now that our currency is worth buttons now. So paying a relatively high price for the food as well as tipping... Not an excuse, I doubt that type would tip if it was $100 to the pound.