When you're listening to a really good song and can't decide what instrument to pretend to play, so you switch up every few seconds. Most common instruments include: lead guitar, rhythm guitar, drums, and keyboard.

I couldn’t care less (but one must keep up appearances, right?)

Like it's solo cousin, air guitar, an air band involves pretending to play musical instruments enthusiastically to recorded music. No actual instruments are involved.

Etymology: Scrubs.

Playing With Your Imaginary Penis

The epitome of wickedness.