Lyric discussion by doortodoor 

Cover art for S-e-x-x-y lyrics by They Might Be Giants

You're going the wrong way with it. It's about someone born with a rare birth defect in which the child has both an x and y chromosone from the male as well as the x chromosone from the female thus making it x-x-y. This gives the child both male and female charectoristics and makes the rest of the song make sence.