I cheated, and searched for some jokes on the interwebs...

What's the difference between a violin and a viola?
There is no difference. The violin just looks smaller because the violinist's head is so much bigger.

What's the difference between a violin and a fiddle?
A fiddle is fun to listen to.

Why are viola jokes so short?
So violinists can understand them.

How do you tell the difference between a violinist and a dog?
The dog knows when to stop scratching.
How do you keep your violin from getting stolen?
Put it in a viola case.

What do a violin and a lawsuit have in common?
Everyone is happy when the case is closed.

Why do people tremble with fear when someone comes into a bank carrying a violin case?
They think he's carrying a machine gun and might be about to use it.
Why do people tremble with fear when someone comes into a bank carrying a viola case?
They think he's carrying a viola and might be about to use it.

Did you hear about the violinist who bragged that he could play 32nd notes?
The rest of the orchestra didn't believe him, so he proved it by playing one.

How many second violinists does it take to change a light bulb?
None. They can't get up that high!

Why is a violinist's fingers like lightening?
They never strike the same place twice!

Why don't viola players suffer from piles (hæmorrhoids)?
Because all the buttholes are in the first violin section.

What's the difference between a fiddle and a violin?
No-one minds if you spill beer on a fiddle.

Why do violinists put a cloth between their chin and their instrument?
Violins don't have spit valves.

Why should you never try to drive a roof nail with a violin?
You might bend the nail.

How do you get two violinists to play in unison?
Shoot one.

A violinist says to his wife, "Oh, baby, I can play you just like my violin."
His wife replies, "I'd rather have you play me like a harmonica!"

Jacques Thibault, the violinist, was once handed an autograph book by a fan while in the greenroom after a concert.
"There's not much room on this page," he said. "What shall I write?"
Another violinist, standing by, offered the following helpful hint: "Write your repertoire."

Isaac Stern was once confronted by a middle age lady after a concert. She gushed "Oh, I'd give my life to play like you!"
"Lady", said Stern acidly, "That I did!"

At Jascha Heifetz's debut at Carnegie Hall in 1917, violinist Mischa Elman stood up at the break and wiping his face, he commented" It's hot in here!" Arthur Rubenstein sitting next to him quipped, "Not for pianists!"

"Haven't I seen your face before?" a judge demanded, looking down at the defendant.
"You have, Your Honor," the man answered hopefully. "I gave your son violin lessons last winter."
"Ah, yes," recalled the judge. "Twenty years!"

To be fair to other musicians:

When a conductor and a watermelon are dropped from a 24 story building, which hits the ground first?
--Who cares?

A man and his son were walking through a cemetery. The boy asked, "Daddy, do they bury two people in the same grave?"
The father said, "Two people? Let me look."
So the father took a look, and sure enough, the marker said, "Here lies a symphony conductor and a humble man."

They call a viola, a bratsche in Germany. Do you know how this came to be?
Because that's the sound it makes when you sit down on it.

The following was contributed by Diane Sullivan who plays violin with the Phoenix Symphony:

How do you get a cello to sound beautiful?
Sell it and buy a violin. (been there, done that)
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How do you get a cellist to play fortissimo?
Write "pp, expressivo" on the music.
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What do you call one pretty good violinist, one better-than-average violinist, one failed violinist, and someone who hates violinists who are all together in the same room? A string quartet.