“What did St. Patrick say to the snakes?”/“He told them to ‘hiss off!’”

A St. Patrick’s Day joke about Saint Patrick is:
 
Q: What did St. Patrick say to the snakes?
A: He told them to “hiss off!”
 
The joke has been cited in print since at least 2001.
 
 
Kidsjokes.co.uk (June 14, 2001)
St Patricks Day Jokes
What did St. Patrick say to the snakes?
He told them to “hiss off”
 
Orange Peel—Citrus Glen Newsletter (Fenruary 2006)
Pg. 4:
St. Patrick’s Day Groaners
Q: What did St. Patrick say to the snakes?
A: He told them to “hiss” off.
 
Sudoku Puzzles
Canuk Greg  From Ottawa, Canada   Supporting Member
17/Mar/07 7:45 AM
(...)
What did St. Patrick say to the snakes?
He told them to ‘hiss off’
 
Twitter
Heather Rowland‏
@heatherrolo
What did St. Patrick say to the snakes? HISS OFF. Hahaha you’re welcome. Happy St. Patrick’s Day.
7:38 AM - 17 Mar 2011
 
Twitter
Frank Bunton‏
@TwistinFrank
What did St. Patrick say to the snakes?
He told them to “hiss off!”
4:45 AM - 11 Mar 2017