“A guy walks into a bar...” is a typical form of what has been called the “bar joke.” A goat version is:

“A goat walks into a bar. The bartender says, ‘We don’t serve kids!’”

“A young goat walks into a bar.  The bartender says, ‘Sorry, we don’t serve kids’” was posted on Twitter on April 2, 2010.


Twitter
Cafe’ On Main CT‏
@CafeOnMainCT
A young goat walks into a bar.  The bartender says, “Sorry, we don’t serve kids” http://bit.ly/9VaIDd
7:14 AM - 2 Apr 2010

Twitter
Technical Writer‏
@TechWriterInfo
A juvenile goat walks into a bar and then the bartender says “Sorry, no kids.”
11:48 PM - 23 Aug 2010

The Morning News (May 13, 2012)
Party Jokes
by Andrew Womack
(...)
So this goat walks into a bar. He goes up to the bartender and orders a beer. The bartender says, ‘Hey, buddy, we don’t serve goats here.’ The goat says, ‘Why not?’ The bartender says, ‘We don’t serve kids.’

Twitter
Paul‏
@Stirgryguy
A baby goat walks into a bar orders a scotch and coke and the landlord says “I don’t serve kids”
12:30 PM - 20 Jul 2013

Twitter
Lee J‏
@Ledge7475
A young goat walks into a bar
The barman says ‘Sorry no kids allowed’
2:36 PM - 20 Jan 2014

Twitter
Tripp‏
@TrippNZ
Replying to @Orcon
@Orcon Goat walks into a bar and asks for a pint. ‘Sorry I can’t serve you’, ‘Why not’ asks the goat. ‘We don’t serve kids’ .#GoatSimPuns
6:44 PM - 25 Mar 2014

Graphic Joke
A goat walks into a bar…
May 3, 2015 by golly
A goat walks into a bar. He goes up to the bartender and orders a beer.

The bartender says, ‘Hey, buddy, we don’t serve goats here.’

The goat says, ‘Why not?’

The bartender says, ‘We don’t serve kids.’

Richard Lederer’s Verbivore
The Top 10 Jokes About Animals In Bars – Bar None
Published May 14, 2016 | By Richard Lederer
(...)
5. A goat walks into a bar, and the bartender says, “I’m sorry, but we don’t serve kids here.”