“A guy walks into a bar…”  is a typical form of what has been called the “bar joke.” A beaver version is:
     
“A beaver walks into a bar. The bartender says, ‘Close the dam door!’”
   
“A beaver walks into a bar. Bartender says, ‘Close the dam door!’” was posted on Twitter by Steve Center on December 28, 2020.
   
       
Yarn
Hey, would you two close the “dam” door?
The Simpsons - The Simpsons Spin-Off Showcase [S08E24] (Originally aired on May 11, 1997.—ed.)
 
Twitter   
Steve Center
@terapinstn
A beaver walks into a bar. Bartender says, “Close the dam door!”
10:36 AM · Dec 28, 2020
   
Twitter
Peter Beetlestone
@PVBeetlestone
A beaver walks in to a bar. The bartender says:“close the dam door!”
8:20 AM · May 19, 2021
   
Twitter
Peter Beetlestone
@PVBeetlestone
A beaver walks in to a bar. The bartender says:“close the dam door!”
2:31 AM · May 19, 2022
   
Twitter
Paul Fox
@PaulFox50854324
Why do beavers all get yelled at by the bartender when they enter the bar?
Because they can never remember to close the dam door!
3:00 PM · Jun 22, 2022
 
Reddit—Dadjokes
Posted by u/Major_Independence82 March 22, 2023
A beaver walks into a bar.
The bartender says, “Close the dam door!”
 
Reddit—Dadjokes
Posted by u/setherooo9 March 27, 2023
A beaver walks into a beaver bar
The bartender says, “Close the dam door.”