I'm mixed race as well,
And it really bothers me when people try to tell me what my ethnicity is. Sometimes people ask, for the most part, when I wear my hair curly people can guess I'm half black, but then they struggle guessing the other half. If my hair is straight people are more open with their guesses.

edit; It also bothers me that people automatically assume things based on skin color. Like, some people I've talked to don't believe me at first when I tell them I'm biracial because I have a medium skin tone. I'm not light, but I'm not dark. I'm just in the middle.