What ARE you?

"The thing that drives me really crazy," Wendy told us, "Is people are always asking me 'what ARE you'. It happens all the time!"
Wendy isn't from another planet. Her family comes from different parts of the world and people are curious about her "pedigree."
Aw big deal, I thought at first. She's getting offended about nothing. The things people get unglued over!
It did get me thinking. Why did it bother Wendy?
Later I ran into George, an old acquaintance. He seemed delighted to see me and acted sincerely interested in what I was up to. Dang, I thought He makes me feel totally accepted. Like a family member. In the club. Teammates.
I thought back to caveman times. You were either accepted as one of the tribe or were considered an outsider. One of them.
A subtext of the chat with George was "I accept you as my peer. You're one of us."
The subtext in "What ARE you" can be interpreted as "What is it about you that makes you not my peer? You're not one of us. " I can see how that would get old very quickly.
At least that's my theory.