there's some loose ends that need to be tied:

-You choose your psychological gender (male, female, androgynous, agender, 3rd gender &c.) as much as your physical gender at birth (male, female or intersex).
-You choose your psychological sexuallity (heterosexual, homosexual (lesbians and gays), assexual, pansexual &c.) as much as your physical sexuallity(same as before) at birth.
-You choose your gender identification (cisgender or transgender) and sexual identification (cissexual or transexual) as much as the place or time you were born.

tl;dr: tumblrinas belive that, for example, a white male can choose to be cissexual (to identify with one's birth sexuality) or women can choose to be bisexual (to be sexually attracted to males and females), so that they (cis men and bi women) can fell superior about it (this is by far a huge über-hipocrisy).