An Irish pun popular on St. Patrick’s Day is:
 
Q: What do you call a diseased Irish criminal?
A: A leper-con (leprechaun).
 
The “leper-con” joke has been cited in print since at least 2002.
 
   
Wonderland Press
BY DE ON SEPTEMBER 26, 2002 IN UNCATEGORIZED
Joke of the Week.
 
Every week, I put a joke in the dept. newsletter. They have been bad and worse. I feel no shame in stealing Lee’s jokes, either.
 
Last Monday’s:
 
What do you call a big group of short elves with a terrible disease?
…A Leper-con.
 
Google Groups: alt.humor.puns
Puns of the Weak 02-21-03
Stan Kegel
2/21/03
(...)
Did you hear about the diminutive criminal from Ireland who contracted Hansen’s disease? He was a leper con.  He’s already lost several fingers, but with any luck each arm won’t fall off. (Gary Hallock)
 
Google Groups: alt.humor.puns
Kid’s Puns of the Weak 03-23-04
Stan Kegel
3/23/04
(...)
What do you call a diseased Irish criminal?
A leper con (Patrick and Marianne)
 
Google Books
Maragold in Sixth
By Bill Sheehan
Lincoln, NE: iUniverse
2007
Pg. 6:
“What do you call a criminal leprechaun that has developed a really bad skin disease?”
 
Maragold shrugged her shoulders, wrinkled her brow, then simply gave up and said, “What?”
 
“You’d call him a leper-con.”
   
Twitter
Mike Stenger‏
@mikestenger
What do you call a diseased Irish criminal? A leper-con
9:28 AM - 17 Mar 2009
 
Twitter
Jess Morgan‏
@MorganBotanical
What do you call a diseased Irish criminal?—> A leper-con!
11:30 AM - 17 Mar 2012
 
Twitter
Emily Knuckles‏
@EmilyKnuckles
What do you called a diseased Irish criminal? A leper-con 🍀💚
4:13 PM - 17 Mar 2016