I play a little guitar, and I catch myself doing this some times. It's just something that some folks cannot help doing... Making funny faces while playing the guitar.
I'll waste no more of your time, I'll direct you to some examples right now.
Some good music, but some pretty funny faces, I must say. Mick Fleetwood does this too, although he plays the drums. I don't like Fleetwood Mac though, so I'll not be posting any such material. Sorry.
Hope you enjoyed this as much as I did!