When people say "My girl", it sounds like you're talking about your daughter, not about a wife/girlfriend. So saying you're having a son with "your girl" sounded pretty damn creepy.
My wife just gave birth to my daughter. In honor of Destiny, we decided not to name her. She will just be referred to as "Daughter". The rumor is that we at one point had a name picked out for her, but had to cut it so we could make the launch date.