“What’s the difference between a dog and a fox?”/“About five drinks.”

In sex slang, a “dog” is an unattractive woman and a “fox” is an attractive woman. A riddle is:
 
Q: What’s the difference between a dog and a fox?
A: About five drinks.
 
The joke has been cited in print since at least the 1980s.
 
     
Google Books
Mademoiselle: The Magazine for the Smart Young Woman
Volume 91
1985
Pg. 12:
As Rose likes to say, “What’s the difference between a dog and a fox? Five drinks.”
   
7 June 1987, Detroit (MI) Free Press, “Yuk Yuks,” Magazine, pg. 23, col. 6:
J. Robert Kirby, Detroit travel agent
Q—What’s the difference between a dog and a fox?
A—Three drinks.
 
Google Books
More of the Straight Dope
By Cecil Adams (Ed Zotti)
New York, NY: Ballantine Books
1988
Pg. 208:
Q: What’s the difference between a dog and a fox?
A: A six-pack.
 
Google Groups: alt.penpals.forty-plus-yrs
What’s the difference between a dog and a fox?
Meredith
1/16/98
5 drinks.
 
Twitter
FΔWΔD ΔFZΔL
@fawadafzal
What is the difference between a dog and a fox?
About 5drinks.
3:17 AM - 5 Apr 2008
 
Twitter
Mark McWilliams
@markmcwilliams
Replying to @PeterBestel
@PeterBestel Just one more!... “What’s the difference between a dog and a fox? About 5 drinks?!” Still don’t get that one! 😉 LOL
4:52 AM - 3 Mar 2009
 
Twitter
/ðiːˈˈɑːdvɑːrk/
@theaardvark
@saronti My favourite #joke: What’s the difference between a dog and a fox? . . . . .  About 10 pints!
4:11 PM - 15 Mar 2009
    .
10 November 2009, The Sun (London, UK), “Have a Laugh,” pg. 13:
WHAT’S the difference between a dog and a fox? About five pints.
DAVE BENNETT Derby
 
Reddit—Jokes
What’s the difference between a dog and a fox?
submitted April 26, 2013 by Myshitstinks
About 6 beers.
 
Google Books
A Prairie Home Companion
Pretty Good Joke Book
Introduced by Garrison Keillor
Prince Frederick, MD: HighBridge, a division of Recorded Books
2015
Pg. ?:
What’s the difference between a dog and a fox?
About eight beers.