It is responsible for when a song gets stuck in your head and won't go away.

There is no known cure for music worms, but some treatments are:
Trying to replace one music worm with that of another song,
Trying to pass on your worm to another person ("host"),
Isolation from all music, TV and other forms of media (including elevators and muzak blaring grocery stores).

When some little bitchboy is acting like a little tiny pee pee poo poo baby and messing up the group plans.