Air guitar is a bona fide option??? I ask because one of my Sims played air guitar once but I'm pretty sure it was a glitch. The whole file was glitched (Sims appearing and vanishing, Sims caught in endless loops -- it was a hot mess).
This particular Sim was NOT a Rock Star; he wasn't even a musician. He just played for his own enjoyment. On night of the biggest glitchfest, he was at a party, playing the guitar, when suddenly the guitar simply vanished (along with several of the guests). In the true spirit of show business ("the show must go on"), he continued to play, even though there was no guitar. Voila, air guitar.
I now have a Hit Movie Composer, and I've never seen her play air guitar. Maybe that animation is based on the Virtuoso trait rather than the choice of career (my musician Sim is not a Virtuoso)?