> that's not how immigrant communities see themselves.

Whoa, who's talking about immigrant families? Immigrant families came from somewhere else. That's their identity, because it's where they came from. But if your family has been here for a few generations, then I have news for you: you're not immigrants!

> I do in fact know the perecentages of my national makeup. Nobles know their ancestry down to the smallest detail, is somebody really tacky for knowing that technically they are 1/4th Italian?

The game of percentages is absurd to begin with. It's one thing to know you have some ancestors from Japan. It's another to say "I am 12.5% Japanese!" What the hell does that even mean? When noble families recognize their ancestry, first off, they don't make ridiculous claims of percentage. No nobleman says "I am 1/16 Catalonian". They'd laugh at you. "You mean to tell me your culture is 1/6 Catalonian?" Second, they don't identify with the culture of an ancestor if it has no presence and reality for them. The British royal family has German roots (and like all European royal families, a complicated web of ancestry spanning virtually all of Europe in some way or another), yet they don't claim to be German or Hessian. It would be absurd. They're the British royal family, and much of them have been the British royal family for some time!

(I do recognize cultural identity as complex, of course, more complex than how many people see it, but it's complex when the cultural dimensions are actually real, not fabricated by the imagination.)

> I don't think attacking somebody's identity is ever fair; it costs you nothing but is everything to them.

But it's not their identity. It's a pretense. If some distant ancestor's cultural origin is everything to someone, then you're proving the absurdity of of the whole thing.

Like I say, it's a socially-accepted form of cosplaying.