I guess I finally have to come right out and ask a question that I had hoped to avoid.
I’m usually pretty up on slang and the current usage of language. But for decades now I have been trying to figure out what the meaning is of the phrase “Who’s your daddy?”, and in what context someone would use it.
I kept hoping that I would eventually hear it used in a context that would give me an unequivocal idea of it’s meaning, but it never happened. So, can anyone clue me in?
I don’t know the answer, but I thought that I would point out the irony of this being your 69th post. 
I asked this same question three months ago. Check here: http://boards.straightdope.com/sdmb/showthread.php?threadid=32157
Hmmmmm I’ve always thought of it as sexual term. Like a males saying to a woman durring sex, “Who’s your Daddy.” As in “Who’s in charge now?” sort of a dominance thing.
Read through the previous thread, and tho two posters mentioned it in a sporting, “Who’s better than you” vein, I have used it and heard it used in a more general sporting term, on the golf course, rolling dice, playing cards, along the lines of “Come to poppa,” or “Baby needs a new pair of shoes.”
And I (and a few others) asked it long before that, so who’s yer daddy now?
http://boards.straightdope.com/sdmb/showthread.php?threadid=12647
The artist formerly known as opus
Attrayant:
Interesting, but I’ve NEVER heard this used in a one-upmanship fashion. I think that the responmdent who said it was short for “sugar daddy” in the thread I started was on the right track. That seems to fit the circumstances I’ve heard. The right answer from the woman would, of course, be “you are”, but the answer is pretty much implied. I still don’t much care for the phrase, and don’t know why it gets used so much on-air.