Inspired by Flamsterette_X’s impressive contributions in this thread, I thought it’d be a good idea to open a separate thread devoted to Bad Musician Jokes. But do I mean jokes about bad musicians or bad jokes about musicians? Both. And to open it up, something that fits both possible definitions at once.
The following concerns a concert harpist at the Boston Symphony Orchestra.
The conductor at the time was William Steinberg, who insisted on very formal rehearsals. Musicians were expected to be early, so that the rehearsal started exactly on time, and wearing a suit and tie.
This harpist was getting tired of the small parts his instrument got in most symphonic works. One evening over drinks, a friend of his named Sam Frank invited the harpist to play at his club.
So the harpist showed up with his harp and played some background music for the early patrons before the band arrived. When the other musicians (a small jazz combo) arrived, they asked the harpist to sit in with them. It was meant as a joke, but he took them up on it.
Soon, the harpist was be-bopping right along with the combo. People were dancing, drinks were flowing, and the music was moving. It was the best gig the harpist had ever been a part of.
Unfortunately, the harpist did not keep track of the time. And when the gig ended, he went to an after-hours club with the other musicians. He eventually stumbles home in the wee hours of the morning. He stumbles into bed without changing, and hits the snooze alarm a few too many times mere hours later.
Eventually he realizes his predicament, rushes to Symphony Hall and hurtles into the rehearsal room just as Steinberg is taking his place.
Steinberg is not impressed. The harpist is unshaven, unshowered, and wearing yesterday’s disheveled clothes. “Please take your place at your instrument,” he instructs. “Speaking of which, where is your instrument?”
“Oh, no!” the horrified harpist exclaims. “I left my harp in Sam Frank’s disco!” 
Thankyou, thankyou, thankyou. Remember to tip your wait staff.
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