Shaver's Disease

A medical condition in which the sufferer experiences convulsions restricted to the arm regions, usually resulting in drum like taps on whatever surface happens to be near. As it is a close relative of tourettes syndrome the sufferer often screams and tells at random intervals subsisting mainly of "what the sack" or pterodactyl screeches.

"What's up with that guy screaming in the corner?"
"Oh he has stage five Shaver's Disease"