Doubting one's Ethnic Value?

Why does America have standards as to what makes you ethnic? Take me for example, I wear braids but get perms. I wear a 'Support Africa' shirt, but I like Evanescense. At my wedding, my groom and I will jump the broom, but we'll have a gourmet dinner. Why do the things I listed above make me (and others like me) too White to be Black, too Black to be White? Why do we, as Americans, have such ridiculous standards as to what's ethnic and what's not? Have you ever had this happen to you?