A few years back I was taking a training class. This involved using computers and working with a client database. The instructor wanted the students to come up with fictional names for the FIRST NAME, LAST NAME fields. Before I found out there is no DELETE option (in the training session), I typed WHOS URDADDY.
For a moment I thought I was clever because it would show up on the projector screen in front of the class, we’d have our laugh, and I would change or delete it right away. So I thought. Instead, the instructor got mad, really mad. It was as if I typed in something really obscene. But I guess this phrase can have an offensive meaning.
One background on it’s usuage can be found on WikiAnswers here, or in this article here. You may also recall the line from the song Time of the Season, "What’s your name? Who’s Your Daddy? Is he rich – like me?"