Chances are good that you've seen at least one of Keenan Cahill's YouTube videos — he's the teenager that lip-syncs to pop songs. To tackle Katy Perry's latest hit "Last Friday Night (T.G.I.F.)", Cahill got some help from the Glee kids. Dianna Agron, Harry Shum Jr., Darren Criss, and Jenna Ushkowitz show off their dance skills as Cahill does the lip-syncing (Dianna is really working that new haircut). Check it out, and tell us how it compares to the star-studded original video.