Pauly D -- Out-Fist Pumped by YouTube PHENOM
He's already been through 50 Cent and Katy Perry ... but now YouTube powerhouse Keenan Cahill -- that kid who lip-syncs with the stars -- is facing off with Pauly D ... with fist pumps of FURY!!!!
![](https://cdn.statically.io/img/imagez.tmz.com/image/ca/16by9/2011/12/16/cae7253bf0985aab88e3f6c1737bd02a_md.jpg)
15-year-old Keenan was diagnosed with a rare genetic disorder when he was a baby -- but he's burned up the Internet with his AWESOME lip-sync videos.
Pauly tells us he APPROACHED Keenan with the idea for this clip -- and Keenan was kind enough to pencil him in.
Check it out -- it's pretty good.