“You can’t eat just one” (“Betcha can’t eat just one”) is a popular slogan for Lay’s potato chips. A riddle is:
   
Q: Why did the sea monster eat five ships that were carrying potatoes?
A: No one can eat just one potato ship.
 
The riddle has been cited in print since at least 1996.
 
   
Google Groups: rec.humor
Potato joke
Dan Reuter
3/18/96
There was a whale in the middle of the ocean that saw two boats loaded with potatoes.  He looked at both of the boats, and before you could say, “Jack Robinson,”  the whale had swallowed both of them.  Why???? Silly, no one can eat just one potato ship!
   
Google Groups:alt.fifty-plus.friends
Two sea monsters
LadyBug
5/23/01
: Two sea monsters were swimming around in the ocean, looking for
: something to do. They came up underneath a ship that was hauling
: potatoes. Bob, the first sea monster, swam underneath the ship,
tipped
: it over and ate everything on the ship.
: A little while later, they came up to another ship, again hauling
: potatoes. Bob again capsizes the ship and eats everything on board.
: The third ship they found was also hauling potatoes and Bob once
again
: capsized it and ate everything.
: Finally his buddy Bill asked him, “Why do you keep tipping over
those
: ships full of potatoes and eating everything on board?”
: Bob replied, “I wish I hadn’t, but I just can’t help myself once I
: start. Everyone knows you can’t eat just one potato ship.”
         
Google Groups alt.humor.puns
Kids Puns of the Weak 06-08-04
Stan Kegel
6/8/04
(...)
Why did the sea monster eat five ships that were carrying potatoes?
No one can eat just one potato ship. (Rosie OąDonnell)
 
Google
Books 
More One Liners, Jokes and Gags
Compiled by Grant Tucker
London, UK: Biteback Publishing
2013
Pg. ?:
Why did the sea monster eat five ships that were carrying potatoes?
No one can eat just one potato ship.
 
Reddit—Dadjokes 
Posted by u/dfj3xxx February 19, 2017
Why did the sea monster eat 5 ships carrying potatoes?
Because you can’t eat just one potato ship.
   
Reddit—Jokes 
Posted by u/like-dinosaurs January 16, 2019
Why did the sea monster eat 6 ships full of potatoes?
Nobody can eat just one potato ship.
 
Twitter 
zee
@VeesAQueen
BUZRO TOLD ME TO TELL MORE OF MY FAMOUS JOKES BC I BEEN LOSING FOLLOWERS SO HERE WE GO
Why did the sea monster eat five ships that were carrying potatoes?
No one can eat just one potato ship.
11:31 AM · Sep 25, 2019·Twitter for iPhone
 
Twitter 
Python Joke Bot
@PythonJokeBot
Why did the sea-monster eat 5 ships filled with potatoes? Because no one can eat just one potato ship.
#joke #jokes #fun #funny #humour #bot #machine_learning #python #AI
9:05 AM · Apr 13, 2020·Python Joke Bot
 
Reddit—3amjokes 
Posted by u/MyJelloJiggles
Why did the sea monster eat five ships that were carrying potatoes?
No one can eat just one potato ship.