That would be Olivia Newton-John's Physical.
Let's get physical, physical....
Alright, that doesn't in anyway have much to do with who I am, except that if ONJ was talking to me, I'd be like "hell yeah!"
It's interesting though. You can look up the #1 song on your birthday like I did by doing a Google search for "Billboard #1 song on [insert date here]". There's a Wikipedia page that lists the songs.
Or try this nifty site where you can find the #1 song on your birthday.
Then just share it with me in the comments below.