They can't find the key, and they never know when to come in.
or
Take the pizza delivery sign off the roof
or
It's someone who knows how to play the bagpipes, but doesn't.
or
You can tuna piano, but you can't piano a tuna
or
Because he's Haydn.
or
He/She keeps trying to stick their fist up your butt.
or
Night manager at McDonalds
or
"This phone is baroque, please call Bach later."
or
Sell it and buy a violin
or
Two flutes playing in unison.
or