A popular St. Patrick’s day riddle has been cited in print since at least 2001:

Q: Did you hear about the leprechaun who worked at the diner?
A: He was a short-order cook!

A slightly different form of the joke was posted on Twitter on March 10, 2015:

Q: What did the leprechaun do for a living?
A: He was a short-order cook!


Kidsjokes.co.uk (June 23, 2001)
St Patricks Day Jokes
Did you hear about the leprechaun who worked at the diner?
He was a short-order cook!

The Blue Mountain Internet Customer Newsletter
St. Patrick’s Day Funnies
by Katrina Moran
March 2005
Q: Where would you find a leprechaun baseball team? In the Little League.
Q: Did you hear about the leprechaun who worked at the diner? He was a short-order cook.

Wilders Security Forums
Q. Did you hear about the leprechaun who worked at the diner?
A. He was a short-order cook!
(...)
Rita, Mar 13, 2005

Watchuseek
Thread: Happy Saint Patrick’s Day
SurferD
March 18th, 2007
(...)
Q. Did you hear about the leprechaun who worked at the diner?
A. He was a short-order cook!

Google Groups: uk.local.south-wales
St Patrick’s day was yesterday
Jane Sullivan
3/18/07
(...)
Q: Did you hear about the leprechaun who worked at the diner?
A: He was a short-order cook…

Twitter
Beverly Schmitt‏
@BeverlySchmitt
Q.  Did you hear about the leprechaun who worked at the diner?
A.  He was a short-order cook!
10:15 AM - 17 Mar 2009

Twitter
Gale Martin‏
@Gale_Martin
Did you hear about the leprechaun who worked at a diner? He was a short order cook. #StPatsDayJokes
7:07 AM - 17 Mar 2012

Twitter
Rachael Kelley‏
@RachaelKelley13
Sign spotted outside a restaurant: “Leprechaun wanted for short order cook.”
8:51 PM - 6 Mar 2013

Twitter
Bear Nation‏
@SHSBearNation
What did the leprechaun do for a living?
(He was a short-order cook!)
10:48 PM - 10 Mar 2015

Facebook
JuWanna the Clown
March 15, 2015 ·
(...)
Q: What job does a leprechaun have at a restaurant?
A: A short-order cook!

FitNHit
St Patricks Day 2016 Sayings: Funny Messages, Quotes, Images to Share on FB Whatsapp
News March 16, 2016 Harjeet
(...)
Q: What did the leprechaun do for a living?
A: He was a short-order cook!

My Town Tutors
St. Patrick’s Day Jokes: St. Patrick’s Day Jokes for Teachers
Posted on March 16, 2016
(...)
6. What did the leprechaun do for a living?… He was a short-order cook!