A popular joke about music critics is:
 
Q: What do you call a guitar player who only knows two chords?
A: A music critic.
 
The joke has been cited in print since at least 1997.
 
 
Google Groups: houston.music
Houston Rock Review Web Site
OTNote
2/20/97
(...)
Q.  What do you call a guitarist that only knows two chords?
A.  A music critic.
 
Google Groups: alt.music.makers.soloact
My friends set these along
Beej&John
10/2/00
(...)
Q: What do you call a guitar player that only knows two chords?
A: A music critic.
 
Google Books
Real Country Humor:
Jokes from Country Music Personalities
By Billy Edd Wheeler
Little Rock, AK: August House Publishers
2002
Pg. XVI:
Q: What do you call a guitar player who only knows two chords?
A: A music critic.
 
Google Books
The Songwriter’s Hook Book
By Jon Batson
Instantpublisher.com
2003
Pg. 11:
Q: What do you call a guitar player that only knows two chords?
A: A music critic.
 
Twitter
The Worship Butthead
‏@WorshipButthead
What do you call a guitarist who only knows 2 chords? A music critic.
2:16 PM - 26 May 2015
   
Twitter
MusicianHumor
‏@JokesBoutMusic
Q: What do you call a guitar player that only knows two chords?
A: A music critic.
2:58 PM - 10 Dec 2015