Music ones
"What kind of air are you blowing down that flute?"

(After a terrible Tchai solo)
Conductor: What the hell was that?
Musician: (deadpan) Jazz.
(Variation on that one for the geeks: "Tippett".)

Two conductors bickering before a concert, one talking about how his technique is better, and how he trained for decades to perfect his upbeat. The other, "Yeah? Well my baton is longer than yours."

"We need a new drumstick. Try (player's) oboe. You'll probably get a nicer sound out of it."

"Mozart was buried a few hundred years ago. That, ladies and gentlemen, was the sound of him decomposing."
(Sivvus trolley collision in the fruit aisle led to a jam, Fri 25 Nov 2011, 9:28, Reply)