What on earth?! How would they possibly even know if the person was a citizen or not? Or if they weren’t, would they not tip people here legally on green cards and work visas? And what does the waiter’s citizenship status have to do with their job performance? Nothing, that’s what. And there are very very few reasons to ever leave less than a 20% tip in any case. None of those reasons have to do with citizenship. Grrr. I hate people that don’t tip.