Science pun for today (Yes I do say this, in class): The red pigment that carries oxygen in your blood is hemoglobin...unless you are a girl. Then it's shemoglobin.
Bwaaaa! Oh yes, that would be "androgynoglobin." "androgenoglobin" = the globin of Mark McGwire, Barry Bonds & co.
And then there's transsexualglobins (y'know: start as one gender and discover you're in fact the other) And travestiglobins (they like to dress up nice!) Niece!