Well this exists.
For those of you who don't spend much time on the Internet, this video posted at the official MLB YouTube page is the parody of the uber popular "What Does the Fox Say?" by Ylvis, a "comedy duo" from Norway.
I can't say I expect this version to be another Internet sensation but a couple of the new lyrics aren't bad:
Rival fan, cheering there
Now there's popcorn in your hair
Your fur is green
You don't smell clean
And the stench brings tears to my eyes
According to the Phillies, "This is the Phanatic’s first music video to land on YouTube."
Watch out Beyonce.