This has been discussed a lot here but I've been doing some introspection on why exactly it bothers me so much when people ask "what I am" when it comes to my race.
Many of the reasons have already been articulated. But one I haven't heard before is this: does anyone else get the impression that the only reason certain people ask you "what you are" is so they know what slurs to avoid when you're around? It's like they can't place me so I'm some kind of racial landmine that could go off at any random slur so to avoid the explosion they ask me straight away "what" I "am."
I've also been considering why it doesn't bother me nearly as much when people of color ask me what I am, and I've realized that it's because (usually) when someone of color asks me this question they are asking because we may have something in common. Whereas when white people ask me, they want to pinpoint why I am not like them. Sometimes it's because if I tell them what race I am, they use it as a shortcut in order to assign stereotypes to me as a way of getting to know me better right off the bat.
I noticed that when my boyfriend's aunt asked me if my last name was Spanish, and when I said yes, she spent the rest of the evening expressing surprise when I told her I wasn't "Hispanic Catholic" and when I told her that I don't cook tacos and burritos. Yes, my last name is Spanish, but no, you still don't know me.