"What's the difference between a DJ and a…

A riddle has been told about a violist (someone who plays the viola), a violinist (someone who plays the violin) and a DJ.

The violist version was printed in the Gasbag (University of Michigan Gilbert and Sullivan Society) in September/October 1991:

Q: What’s the difference between a violist and a shaggy dog?
A: A shaggy dog knows when to stop scratching.

The violinist version was printed in The Arizona Daily Star (Tucson, AZ) on May 13, 1995:

Q: What’s the difference between a violinist and a dog?
A: The dog knows when to stop scratching.

The DJ version was posted on Twitter by Mick_Shrimpton on December 31, 2008:

Q: What’s the difference between a DJ and a dog?
A: The dog knows when to stop scratching.

Google Books
September/October 1991, Gasbag (University of Michigan Gilbert and Sullivan Society), “Viola II” administered by David Goldberg, pg. 19, col. 3:
Q: What’s the difference between a violist and a shaggy dog?
A: A shaggy dog knows when to stop scratching.

Google Groups: alt.music.filk
2 of 3: obnoxious jokes
Joe Bethancourt
Apr 10, 1992, 11:07:46 AM
(...)
What’s the difference between a violin and a dog?
The dog knows when to stop scratching…..

Google Groups: rec.humor
Canonical List Of Music Humor 2/3
Two More Ron’s Don’t Make A Wright
Aug 3, 1994, 7:40:06 AM
(...)
What is the difference between a dog and a viola?
The dog knows when to stop scratching.

Newspapers.com
10 August 1994, Los Angeles (CA) Times, “On TV, Music Comes Fresh From the Can” by Tom Hensley. pg. E2, col. 2:
I have never publicly stated that the difference between a violist and a dog is that the dog knows when to stop scratching.

Newspapers.com
13 May 1995, The Arizona Daily Star (Tucson, AZ), “StarNet—Music jokes,” pg. 2A, col. 3:
What’s the difference between a violinist and a dog?

The dog knows when to stop scratching.

Google Books
The Musician’s Joke Book:
Knowing the Score
By Nancy J. Groce
London, UK: Schirmer Trade Books
1996
Pg. ?:
What’s the difference between a violist and a dog? A dog knows when to stop scratching.

Google Groups: alt.humor
Drummer Jokes
Rick Keller
Oct 24, 1999, 3:00:00 AM
(...)
What’s the difference between a violist and a dog?
The dog knows when to stop scratching.

18 January 2004, Sunday Herald-Sun (Melbourne, Victoria), “Folk” by Bryan Patterson, pg. E14:
HOW do you tell the difference between a fiddle player and a dog? The dog knows when to stop scratching.

Twitter
Mick_Shrimpton
@Mick_Shrimpton
What’s the difference between a DJ and a dog? ...The dog knows when to stop scratching…
6:25 PM · Dec 31, 2008·Twitter Web Client

Twitter
rui da silva
@ruidasilva
What’s the difference between a violist and a dog? The dog knows when to stop scratching.
10:24 AM · Jul 1, 2009·Twitter Web Client

Twitter
YesYechYes
@sriharsha73
How do you tell the difference between a violinist and a dog?
The dog knows when to stop scratching.
2:20 AM · Aug 25, 2009·Twitter Web Client

Twitter
DJNEGRITONY
@DJNEGRITONY
What’s the difference between a DJ and a dog? The dog knows when to stop scratching!
3:34 PM · Apr 21, 2010·Twitter Web Client

Twitter
The Punfisher
@ThePunfisher
What’s the difference between a DJ and a dog? The dog knows when to stop scratching #LOL
12:04 PM · Sep 26, 2017·The Social Jukebox

Twitter
MusicianHumor
@JokesBoutMusic
How do you tell the difference between a violinist and a dog?
The dog knows when to stop scratching.
11:53 AM · Sep 12, 2021·twittbot.net

Twitter
Lorraine Jo King
@lahlahbean
#tuesdaytitters
How do you tell the difference between a violinist and a dog?
The dog knows when to stop scratching.
6:05 AM · Sep 14, 2021·Twitter for iPhone

“What’s the difference between a DJ and a dog?”/“The dog knows when to stop scratching.”