As long as we're on the subject of dumb musician jokes....
Q. How can you tell if the concert stage is level?
A. The drummer is drooling out of both sides of his mouth.
Q: What do you do with a bad musician?
A: Give him two sticks, put him at the back, and call him a drummer.
Q: What if he's a bad drummer?
A: Take away one of the sticks, put him up front, and call him a conductor.
(I have great respect for musicians, but I just thought this was funny!)