When a pianist gets so addicted to playing a piano piece that he starts playing air piano non-stop with his fingers at other locations(Desk, sofa, school, anywhere that's not his piano.)
When the conditions worsens,
the pianist does this involuntarily. The incessant tapping proves annoying to the surrounding others, but also to the pianist himself, usually.
It's
essentially an
equivalent of an earworm, but in a piano context.
Homie: DUDE stop tapping your fingers. It's SO annoying!
Pianist : Damn, sorry homie. I've been tapping my fingers, imagining that I'm playing
Moonlight Sonata Movement 3 literally
everywhere.
Homie: You've totally caught an pianoworm, man. You needa stop
playing piano.