A popular St. Patrick’s Day shamrock riddle is:
 
Q: Why do people wear shamrocks on St. Patrick’s Day?
A: Regular rocks are too heavy.
 
“Why do people wear shamrocks on St. Patrick’s Day? Real rocks would look funny” was cited in 1996. The punchline “Regular rocks are too heavy” has been cited in print since at least 2001.
 
 
Wikipedia: Shamrock
A shamrock is a young sprig of clover, used as a symbol of Ireland. Saint Patrick, Ireland’s patron saint, is said to have used it as a metaphor for the Christian Holy Trinity. The name shamrock comes from Irish seamróg [ˈʃamˠɾˠoːɡ], which is the diminutive of the Irish word for clover (seamair) and means simply “little clover” or “young clover”.
 
Kith and Kin (Marshfield Area Genealogy Group, Marshfield, WI)
March/April 1996
Pg. 5:
HOW IRISH ARE YOU?
TEST YOUR I. Q. (IRISH QUOTIENT)
(...)
2. Why do people wear shamrocks on St. Patrick’s Day?
Answers:
2. Real rocks would look funny.
 
Google Groups: alt.fifty-plus.friends
Groaners for St. Pat’s day
BillB (FL/NC)
3/17/01
Q. Why do people wear shamrocks on St. Patrick’s Day?
A. Regular rocks are too heavy.
 
Google Groups: in.bizarre
Saint Paddy’s Day Humor
.(JavaScript must be enabled to view this email address)
3/17/01
LOL! Just had to share these…just for the “groaners” among you. 😉
Saint Patty’s Day Groaners
 
Q.  Why do people wear shamrocks on St. Patrick’s Day?
A.  Regular rocks are too heavy.
   
16 March 2003, Toronto (ON) Star, pg. D16:
3. Why do people wear shamrocks on St. Patrick’s Day?
(because regular rocks are too heavy!)
 
Google Groups: alt.humor.puns
Kid’s Puns of the Weak 03-23-04
Stan Kegel
3/23/04
(...)
Why do people wear shamrocks on St. Patrick’s Day?
Regular rocks are too heavy. (Candy Silver)
 
Wilders Security Forums
Let’s Have Some Irish Jokes, Proverbs and Toasts
Q: Why do people wear shamrocks on St. Patrick’s Day?
A: Regular rocks are too heavy.
(...)
Rita, Mar 15, 2005
 
Twitter
Tom Cahillane‏
@dmcscorp
Q: Why do people wear shamrocks on St. Patrick’s Day?
A: Regular rocks are too heavy.
www.alcoholichumor.com
7:02 PM - 9 Mar 2009
 
Google Books
St Patrick’s Day Jokes
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
Why do people wear shamrocks on St. Patrick’s Day?
Regular rocks are too heavy.
 
My Town Tutors
St. Patrick’s Day Jokes: Top 10 St. Patrick’s Day Jokes
Posted on March 17, 2015
(...)
7. Why do people wear shamrocks on St. Patrick’s Day? …. Regular rocks are too heavy.