“What do you call a gay milkman?”/“A dairy queen.”

Dairy Queen is a chain of soft-serve ice cream and fast-food restaurants. A riddle has been printed on an image:
   
Q: What do you call a gay milkman?
A: A dairy queen.
 
The joke—often regarded as offensive—has been cited in print since at least 1983.
   
       
Wikipedia: Dairy Queen   
Dairy Queen, often abbreviated DQ, is a chain of soft serve ice cream and fast-food restaurants owned by International Dairy Queen, Inc., a subsidiary of Berkshire Hathaway. International Dairy Queen, Inc., also owns Orange Julius and Karmelkorn.
 
The first DQ restaurant was located in Joliet, Illinois. It was operated by Sherb Noble and opened for business on June 22, 1940. It served a variety of frozen products, such as soft serve ice cream.
     
Google Books
Totally Tasteless:
The collected works (so far) of Blanche Knott
By Blanche Knott
New York, NY: Ballantine Books
1983
Pg. 165:
What do you call a gay milkman?
A Dairy Queen.
 
4 April 1984, Sydney (Australia) Morning Herald, “Carlyon on Sport,” pg. 44, col. 2:
Bob told us about the gay milkman (yes, the dairy queen).
     
26 June 1985, Burlington (VT) Free Press, “Ristau Scolded for Jokes” by Sarah Wilson, pg. 1B, col. 3:
Before introducing some of the speakers, he made jokes referring to a braless woman, and to a man carrying a sign saying “dairy queen.” to show he was a gay milkman.
 
8 April 1988, The Plain Dealer (Cleveland, OH), “Hey comic! Sit down with the amateurs” by Debbi Snook, pg. 21, col. 1:
“I used to think a Dairy Queen was a gay milkman,” he (Jack Matzye—ed.) says.
 
Twitter
Shaleen Manocha‏
@shaleen007
Q: What do you call a gay milkman?
A: A dairy queen.
6:20 AM - 9 Jul 2009
   
Reddit—Jokes
what do you call a gay milkman
submitted April 22, 2015 by wanttono
a dairy queen ....
COMMENTS
CAN_ZIGZAG
HOMOgenized
 
Reddit—Jokes
What do you call a gay milkman?
submitted January 4, 2017 by underruss
A dairy queen.
   
Twitter
new year new dad jokes‏
@dadtellsjokes
What do you call a gay milkman?
A Dairy Queen
8:15 AM - 9 Oct 2017
 
Reddit—Jokes
What do you call a gay milkman?
submitted January 9, 2018 by gingerbread_homicide
A dairy queen