A joke about the viola is:
   
Q: How do you make a violin sound like a viola?
A: Sit in the back and don’t play.
 
The joke was posted on the newsgroup alt.music.filk on April 10, 1992.
   
“How do you make a violin sound like a viola?”/“Play in the low register with a lot of wrong notes” is the viola joke with a different punchline.
 
     
Google Groups: alt.music.filk
2 of 3: obnoxious jokes
Joe Bethancourt
4/10/92
(...)   
How do you make a violin sound like a viola?
Sit in the back and don’t play.
 
Google Groups: rec.humor
Music Jokes
Perry Tarantine
6/12/92
(...)
How do you make a violin sound like a viola?  Sit in the back and don’t play.
 
Google Groups: rec.humor
Canonical List Of Music Humor 2/3
Two More Ron’s Don’t Make A Wright
8/3/94
(...)
How do you make a violin sound like a viola?
Sit in the back and don’t play.
  or
Play in the low register with a lot of wrong notes.
 
Google Groups: rec.humor
VIOLA JOKES
Fil Feit
10/6/94
(...)
Q:  How do you make a violin sound like a viola?
A1: Sit in the back and don’t play.
A2: Play in the low register with a LOT of wrong notes.
 
Google Books
The Musician’s Joke Book:
Knowing the Score
By N. J. Groce
London, UK: Schirmer Trade Books
1996
Pg. ?:
How do you make a violin sound like a viola? Sit in the back and don’t play.
     
Google Books
The Best Musicians’ Jokes
By Bruno Kassel and Carlo May
Pacific, MO: Mel Bay Publications, Inc.
2005
Pg. 30:
How do you make a violin sound like a viola?
Sit at the back and don’t play.
 
Twitter
guadalupe_stein‏
@guadalupe_stein
Q: How do you make a violin sound like a viola? A: Sit in the back and don’t play.
11:47 AM - 27 Nov 2009
 
Google Books
The Musician’s Joke Book
By Jim Green
London, UK: Omnibus Press
2010
Pg. ?:
Q: How do you make a violin sound like a viola?
A: Sit in the back and don’t play.
 
Q: ...And another way to make a violin sound like a viola?
A: Play in the low register with a lot of wrong notes.
   
Google Books
Sensible Nonsense.. Frank’s Comic Pack:
Humour Pack Series
By Frank Paul
BookBaby
2014
Pg. ?:
Q: How do you make a violin sound like a viola?A: Sit in the back and don’t play.
 
Twitter
Lucky Score‏
@LuckyScoreNet
Q: How do you make a violin sound like a
viola?
A: Sit in the back and don’t play.
#Joke from #MusicJokes in #Jokes, #Humor and #Satire
4:42 PM - 24 Oct 2017