“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” A tennis ball version is:
 
“A tennis ball walks into a bar/restaurant. A bartender/waiter asks, ‘Have you been served?’”
       
The bar version was posted on Twitter on March 24, 2012. The restaurant version was posted on Reddit—Jokes on June 26, 2017.
     
 
Twitter
John Collins‏
@HolyDalek
A tennis ball walks into a bar…...The barman says,“Have you been served?”
1:21 PM - 24 Mar 2012
 
Twitter
sickipediabot‏
@sickipediabot
A tennis ball walks into a bar.
The barman says, “Have you been served?”
2:58 PM - 24 Mar 2012
 
Facebook
Hey how’s life? Well… ask life?
March 24, 2012 ·
A tennis ball walks into a bar.
The barman says, “Have you been served?”
 
Facebook
‎Mitchell Ide‎ to Dad Jokes
September 25, 2012 ·
A tennis ball walks into a bar.
The barman asks: Have you been served?
 
Twitter
Chris Heaton-Harris‏
@chhcalling
A tennis ball walks into a bar. The barman looks at it and says: “Have you been served?”
2:00 AM - 27 Jun 2014
 
Reddit—Jokes
A tennis ball walks into a restaurant….
submitted June 26, 2017 by velvethadron
a waiter asks: “Have you been served?”
 
Twitter
Living Sarcasm‏
@SarcasmLiving
A tennis ball walks into a restaurant….
a waiter asks: “Have you been served?”
7:35 AM - 26 Jun 2017