“When do burgers quit their jobs?”/“The day they decide to meat loaf.”

A burger riddle is:
 
Q: When do burgers quit their jobs?
A: The day they decide to meat loaf.
     
The joke was printed in the book 101 Hamburger Jokes (1978) by Phil Hirsch.
 
 
Google Books
101 Hamburger Jokes:
Meaty Jokes to be Devoured with Relish
By Phil Hirsch
New York, NY: Scholastic, Incorporated
1978
Pg. 76:
When do burgers quit their jobs?
The day they decide to meat loaf!
   
funnyjoke.com.au
Category: Burger jokes
Date Added: 10/10/2007
Joke: When do burgers quit their jobs?The day they decide to meat LOAF!
 
Twitter
Bollywood Sargam‏
@bollywoodsargam
Burger jokes - 2270 Joke: When do burgers quit their jobs?
The day they decide to meat LOAF! .... http://twurl.nl/tlhpvh
12:31 PM - 21 May 2009
   
Twitter
Garret Sheriff‏
@grnaa73
When do burgers quit their jobs? The day they decide to meat LOAF!
8:13 PM - 25 Jun 2012
   
Twitter
Kua ‘Aina NI‏
@KuaAinaNI
#FridayFunny When do #burgers quit their jobs?
The day they decide to meat LOAF!
6:30 AM - 29 Jul 2016
 
Twitter
Lucky Score‏
@LuckyScoreNet
When do burgers quit their jobs?
The day
they decide to meat LOAF!
#Joke from #BurgerJokes in #Jokes, #Humor and #Satire
5:54 PM - 4 Feb 2018