He decomposes.
or
He/She keeps trying to stick their fist up your butt.
or
Sell it and buy a violin
or
Fo Drizzle!
or
Man blows into it, but God only knows what comes out
or
When you toss a banjo in the garbage and it hits an accordion.
or
"Would you like fries with that?"
or
No, but hum a few bars and I'll fake it.
or
One who knows how to play the saxophone, but doesn't!
or
They can't find the key, and they never know when to come in.
or