A classic swimming pool joke has been cited in print since at least 1993. A lifeguard tells a swimmer that he’s banned for peeing in the pool. “But everyone pees in the pool!” the swimmer pleads. “Yes,” says the lifeguard, “but not from the high diving board!”
       
The joke has been printed on several images.
 
   
Google Books
Uncle Homer’s Outdoor Chuckle Book:
A rare catch of folksy jokes, quips, cartoons, and keeper memories
By Homer Circle
Lakeland, FL: Larsen’s Outdoor Pub.
1993
Pg. 110:
Guest: “Why heck, every one pees in the pool, you know that.” Lifeguard: “Yes, I know, but not from the diving board!”
 
Google Groups: alt.folklore.urban
NFJ: ARRgghH! (was Re: Peeing in Pool)
Phil Gustafson
4/4/94
(...)
“ORSON!!  Quit peeing in the pool!”
 
“But, my good man, _EVERYONE_ pees in the pool.”
 
“Not from the diving board, Orson!”
 
Google Groups: rec.humor
High Diving Board
Bob F
10/29/96
One day Dirty Johnny’s Mom gets a call from the manager of the public swimming pool.
 
“Maam” He syas “This is the manager of the pool. I am calling to inform you that your son is barred from the pool for the rest of the summer.”
 
“My God.”, she replies. “what has he done now”
 
“Well, we caught him peeing in the pool.”
 
“But every kid pees in the pool.” she says.
 
“Not from the high diving board they don’t”
 
22 May 1998, The Jewish Press (Omaha, NE), “Focus on Issues: What’s so funny in Israel?” by Ronnie Caplane, pg. 4:
A life guard orders Bibi Netanyahu to get out of the pool.
 
“Why are you ordering me to get out?” Netanyahu asks.
 
“Because you’re peeing in the pool,” says the life guard.
 
“Why pick on me? Everyone’s peeing in the pool,” says Netanyahu.
 
“Yes,” says the life guard. “But not from the diving board.”
       
12 January 2001, The Herald (Glasgow, Scotland), “Diary” by Tom Shields & Ken Smith, pg. 24:
The old jokes at home
WE were just wondering how old this joke is. It’s the little boy on a class trip to the swimming baths who is bawled at by the attendant: “You’re not allowed to pee in the pool. You’re getting reported to your teacher.”
 
But the boy protests: “Come on, everyone pees in the pool.”
 
“Aye,” says the attendant, “But not from the diving board.”
 
Yes, you’re right. It’s very old indeed.
 
Google Books
The Penguin Book of More Canadian Jokes
By John Robert Colombo
Toronto, ON: Penguin Canada
2003
Pg. 30:
Pool Manners
A guest registered at a fancy hotel in Calgary is enjoying the use of the swimming pool when the manager appears and tells him quite bluntly to get out of the pool. When the guest asks the reason, the manager says, “Because you peed in the pool.” Well,” replies the guest, “lots of people do that.” “True,” answers the manager, “but not from the diving board.”
 
Twitter
David Moulton‏
@exframebuilder
I got into trouble at school for peeing in the pool…Problem was I did it from the high diving board
6:16 AM - 26 Jul 2009
 
Twitter
Brian Sailer‏
@bsailer
Lifeguard: Stop peeing in the pool.
Guy: Why, everyone does it?
Lifeguard: Not from the diving board!
3:58 PM - 25 Aug 2009
 
Reddit—Jokes
I got kicked out of a pool for peeing in it
submitted November 5, 2017 by user7526
The lifeguard started yelling, telling me to stop.
“But all the little kids do it too!” I yelled back.
“But not while standing on the diving board!”