“It was so hot in New York that I saw squirrels fanning their nuts”

Television’s Late Show with David Letterman (1993-2015) was based in New York City, and there were many New York City jokes. David Letterman told this joke in July 29, 1999, as posted on the newsgroup rec.humor on July 30, 1999:
     
“It’s so hot, I saw squirrels fanning their nuts.”
   
 
Google Groups: rec.humor
“It’s so hot outside…..”
Bruce Tilton
7/30/99
Major M wrote:
It’s so hot, I saw squirrels fanning their nuts.
(sorry, all credit goes to Dave Letterman (Bruce Willis); last night…)
       
Google Groups: alt.fan.authors.stephen-king
It’s hot!
Satwylt23
7/31/99
It’s so hot, I saw a squirrel fanning his nuts.
 
Google Groups: GoodiesGalore
How hot is it in Iowa (not sure it is just Iowa)
Deb S
8/4/06
Other recipients: .(JavaScript must be enabled to view this email address)
How Hot Is It In Iowa (Not sure it is just Iowa)?  It’s So Hot That…...
   
ALL THE CORN STARTED POPPING AND FLYING THROUGH THE AIR.
   
IT’S SO HOT, I SAW SQUIRRELS FANNING THEIR NUTS…...😊
     
Twitter
Sarah Sampsel
@sarahsampsel
It’s so hot… I saw squirrels fanning their nuts.
11:51 AM - 6 Jun 2008
 
Twitter 
Ra5ph
@freakin_ralph
It’s so hot…I saw a squirrel fanning his nuts…
4:53 PM - 4 Jul 2009
   
Twitter
SUZUKI6FT1
@YES_IM_6FT1
Replying to @DanielMaldonado
@DanielMaldonado RT It’s so hot in NYC today, I saw a squirrel fanning his nuts!
12:58 PM - 17 Jul 2009
 
25 July 2010, Fresno (CA) Bee, “It’s So Hot” by David Mas Masumoto, pg. B5:
You saw squirrels fanning their acorns.
 
Twitter
Pauline Lamirante
@paulinelamirant
Replying to @TheRock
@TheRock The heat and humidity are kicking my ass today! It’s so damn hot, I saw a squirrel fanning his nuts!
5:48 PM - 22 Jul 2011
 
Twitter
Piney McKnuckle
@PineyMcknuckle
Replying to @IcecoldDavis
how hot is it today? so hot I saw a squirrel fanning his nuts in Central Park
(David Letterman is seen laughing and clapping.—ed.)
7:34 PM - 19 May 2017
 
Twitter
Ken Cole 🚚 💨
@DJ_Goose1
It’s so hot, I saw squirrels fanning their nuts.
3:20 PM - 15 Jun 2018 from St Louis, MO