Air guitar is old fashioned now. I realized this thanks to my vampire sim Veronica. Take a look!
That somehow happened when I used Twallan's mastercontroller to switch to one of her friends who was visiting at the time. The upright bass rendered itself again when I switched back. I don't think it's Twallan's fault though, it's probably my MacBook's integrated graphics card.
Unlike other glitches in The Sims, this one provided some laughs. As long as it doesn't happen all the time it'll be more amusing than annoying.