A mental disorder.
Hmm. I'm going to go out on a limb here: if we can choose to be any gender we want, why not what race/ethnicity we are? I mean, I was born white, but I think I really identify as black. I just feel that I really have a lot in common with African-Americans. Hell, I could even wear makeup to make me look the part, and maybe someday they'll come up with a pigmentation-altering process to make me look the part.
Cuz I can be what I want, right?