Keenan Cahill Dominates YouTube Again With the Cast of Glee [VIRAL VIDEO]

You've got to envy Keenan Cahill, the lip-"synching" YouTube sensation who's performed with huge names such as 50 Cent and Katy Perry -- and here with Glee stars Harry Shum Jr., Dianna Agron, Darren Criss and Jenna Ushkowitz -- in dozens of tremendously popular YouTube video hits.

It doesn't seem to matter that Keenan, who seems to be coping well with Maroteaux-Lamy syndrome, hardly has any idea what the lyrics are to this catchy tune, Katy Perry's "Last Friday Night (T.G.I.F.)."