“A guy walks into a bar…”  is a typical form of what has been called the “bar joke.” A sheep version is:
     
“Two sheep from Boston walk into a baaaaaaa.”
     
The sheep were going to say “baaa,” but, being from Boston, it adds certainty that they would drop the “r” and say “baaa” and not “bar.”
   
“Two sheep from Boston walk into a baaaaaa…” was posted on Twitter by Trojancountry99 on June 15, 2022. “Two Sheep from Boston walk into a Baah” was posted on Twitter by Shamanomenon on December 11, 2022. “Two sheep from Boston walk into a baaaaaaa” was posted on Reddit—Oneliners on April 20, 2023.
   
“Two sheep walk into a baaaaaa” is a similar bar joke.
     
   
Twitter
Trojancountry99
@trojancountry99
Joke should’ve been.. “Two sheep from Boston walk into a baaaaaa…”
8:40 PM · Jun 15, 2022
   
Twitter
Shamanomenon
@Shamanomenon_WW
Two Sheep from Boston walk into a Baah
3:00 PM · Dec 11, 2022
   
Twitter
Jake Wiskerchen
@jakewisk
So these two sheep from Boston walk into a baaaa…
7:41 PM · Feb 23, 2023
 
Reddit—Oneliners
Posted by u/boitrubl April 20, 2023
Two sheep from Boston walk into a baaaaaaa
   
Twitter
𝕐𝕠𝕦𝕟𝕘 𝕄𝕚𝕤𝕖𝕣𝕪 𝕂
@YoungMiseryK
Two sheep from Boston walk into a baaaaaa
9:41 AM · Apr 20, 2023