It's called "Piano Man II" by Justin Bua. I wrote a little song inspired by it and its (omni)presence at MCD. You should sing it to the tune of any diabetes testing kit commercial jingle you can recall.
Whachu want, baby?
A four-piece fo yo kid?
And you want a milk?
Well we ain't got none of that shit!
But how 'bout some heroin?
Woo-hoo! I said some heroin.
Well I ain't got no f*ckin' nuggets -
How 'bout some heroin fo yo kid?