“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” “A horse walks into a barn” is an anti-joke.
 
“A horse walks into a barn and says “Hay!’” was posted on Twitter by Dee Costa on December 4, 2009. “A horse walks into a barn and the barman says ‘Why the wrong place?’” was posted on Twitter by Ryan Mardy Land on August 24, 2010. “Originally it was just ‘A horse walks into a barn’, but somewhere in the Middle Ages the n was dropped and it became the joke we know today” was posted on Twitter by MꙬse Allain on February 17, 2015.
 
       
Twitter     
Dee Costa
@DeeCosta
A horse walks into a barn and says “Hay!”
6:04 PM - 4 Dec 2009
   
Twitter
Ryan Mardy Land
@Presshardy
A horse walks into a barn and the barman says “Why the wrong place?”
7:19 AM - 24 Aug 2010
 
Reddit—Funny
Horse jokes (self.funny)
submitted February 10, 2012 by a9u1tar1st
So a horse walks into a barn…
           
Twitter
Bucky Isotope
@BuckyIsotope
A horse walks into a barn. Why the long face says the cow. Evolution says the horse. Now stuff your flat nose back in the hay and stfu.
11:55 PM - 17 Aug 2013
 
Twitter
🇸🇪 Tomas 🇸🇪
@M0by_Duck
A horse walks into a barn
After all these years, he finally got it right.
4:12 AM - 14 Nov 2013
 
Twitter
Brian Bilston
@brian_bilston
A horse walks into a barn, goes up to the barntender and says “Why so baleful?”
“A wonderful tweet” The Times
“Wowzers!” New Statesman
12:29 PM - 21 Jan 2014
 
Twitter
MꙬse Allain
@MooseAllain
Originally it was just ‘A horse walks into a barn’, but somewhere in the Middle Ages the n was dropped and it became the joke we know today.
5:31 AM - 17 Feb 2015
 
Reddit—AntiJokes
A horse walks into a bar (self.AntiJokes)
submitted May 19, 2015 by hey-girl-hey
Wait, that’s not right…a barn. A horse walks into a barn.
 
Twitter
MꙬse Allain
@MooseAllain
Originally it was just ‘A horse walks into a barn’, but somewhere in the Middle Ages the n was dropped and it became the joke we know today.
12:20 PM - 29 Sep 2016
     
Twitter
jonny sun
@jonnysun
a horse walks into a barn. wait, why am i here says the barkeep
8:49 PM - 14 May 2017
 
Reddit—Jokes
A horse walks into a bar
submitted May 26, 2017 by RedClover2321
I’m sorry, typo, I meant BARN. A horse walks into a barn after a long day working the farm.
 
Reddit—Jokes
A horse walks into a barn
submitted September 20, 2018 by philb087
A horse walks into a barn
The Barntender says, “Hay, the usual?”