i can't comment on those who think this song is about something sexual.
i have no comment at all regarding anything relating to sex.
however, i have been thinking about this... heir apparent = the one who is supposed to inherit something, this has nothing to do with the lyrics of the song, simply the title. i am an only child, i don't have any brothers or sisters or even step-siblings. no kinds of siblings at all. my father has passed away and my mother has had a histerectomy (sp?), i was the only child produced between my mother and father, and i will never have any "siblings". so, in my family, as the last living male with my family's genes or whatever, i feel that the tiltle "heir apparent" has some meaning to me personally, as i'm supposed to be the only one to carry on my family name, though since i'm too stupid or whatever to get a gf let alone father a child, i feel that i am the so-called "heir apparent" of my family.