There's something satisfyingly self-referential about watching talented musicians try to play their own music in Rock Band and Guitar Hero. Especially when they're worse than you.
Here's a list of every video I could find. Let me know if I missed any.
Anthrax's Scott Ian, "Madhouse" at Best Buy
"You suck. You're going to have to write easier songs... 20 years ago."
Rush, "Tom Sawyer," backstage at the Colbert Report
KISS's Gene Simmons, Tommy Thayer and Eric Singer, "Detroit Rock City"
Dragonforce's Sam Totman and Herman Li, "Through the Fire and the Flames"
My Chemical Romance's Gerard Way, "Dead"
Metalocalypse's Brendon Small, Tommy Blacha, "Thunderhorse"
Jonathan Coulton, "Still Alive"
Backyard Babies, "Minus Celsius"
Joe Perry from Aerosmith talks about the difficulty of learning Guitar Hero for guitarists. "I've talked to a lot of guitarists who've played this, and all the older guys get to the first basic level and then it splits off. Then your gameplaying skills come in, because you have to play the game like it's one of those other kinds of games."
South Park's Guitar Queer-O. "Real guitars are for old people."