“If life hands you lemons, make lemonade” is an old saying from the early 1900s. There have been many jocular variations.
 
“When life gives you lemons, squirt someone in the eye” is a jocular saying that has been printed on many images. “When life gives you lemons, squeeze them in people’s eyes” has also been printed on many images.
 
“When somebody hands you a lemon, squeeze it” was cited in 1907. The book When Life Gives You Lemons, Squirt Back! was published in 1993. “If life gives you lemons, squirt the juice into other people’s eyes” was posted to the newsgroup alt.tv.sliders in August 1996. “When life gives you lemons squeeze them into a squirtgun and shoot at your neighbor’s eye” was posted to the newsgroup alt.games.dune-ii.virgin-games in March 1998.
 
“When life gives you lemons, squirt someone in the eye” was cited on Twitter on January 24, 2009 and credited to Cathy Guisewite, who drew the comic strip Cathy from 1976 until 2010. However, there is no evidence that Guisewite originated the saying.
 
     
19 January 1907, Montgomery (AL) Advertiser, “Driftwood” by Phil H. Armstrong, pg. 4, col. 6:
When somebody hands you a lemon, squeeze it.
 
OCLC WorldCat record
When life gives you lemons, squirt back!
Author: Sandra Jones Campbell
Publisher: Indiana Rocks Beach, Fla. : C.O.P.E., Inc., ©1993.
Edition/Format:   Print book : English
   
13 September 1993, St. Petersburg (FL) Times, “Business Digest” by Christina K. Cosdon, sec. 8, pg. 6:
Sandra Jones Campbell, president of COPE of Indian Rocks Beach, is the author of a recently published book, When Life Gives You Lemons, Squirt Back!. It’s available at some area businesses and bookstores. The book deals with handling job loss, death, family or personal health problems, depression, divorce and natural disasters.
 
Google Groups: alt.tv.sliders
Why do the Sliders have to wait for the timer?
Kusader
8/10/96
(...)
TOP THREE TAGLINES
I could do that but I don’t wanna.
Did anyone see a fat, bald, naked Tibetan man run through here with my tagline?
If life gives you lemons, squirt the juice into other people’s eyes.
   
Google Groups: rec.games.board.ce
Cosmic Encounter - Major Flaw
Val Kartchner
3/26/97
(...)
Remember:  If life gives you lemons, squirt lemon juice in your opponents’ eyes and take their planet.  😊
 
Google News Archive
21 August 1997, Sarasota (FL) Herald-Tribune, “‘To reach our legal defense team, press 1’” by Gordon Russell, pg. 1D, col. 2:
When life gives you lemons, squeeze them in your tormentor’s eyes.
 
Then, laugh like hell.
   
2 February 1998, St. Petersburg (FL) Times, “Band on a Run” by Eric Deggans, pg. 1D:
Not that the band has abandoned its irreverent attitude, spicing the rocker Fear with lines like “When life gives you lemons/squeeze them in your eyes.”
   
Google Groups: alt.games.dune-ii.virgin-games
New Screenshots
John D. Young
3/27/98
(...)
When life gives you lemons squeeze them into a squirtgun and shoot at your neighbor’s eye.
 
Google Groups: alt.andy.whine.whine.whine
out of context
GlowElf
3/2/99
(...)
If life gives you lemons, squeeze the juice into a watergun and shoot other people in the eyes.
 
Google Books
Man Walks into a Bar:
Over 6,000 of the Most Hilarious Jokes, Funniest Insults and Gut-Busting One-Liners
By Stephen Arnott and Mike Haskins
Berkeley, CA: Ulysses Press
2007
Pg. 454:
If life gives you lemons, squeeze the juice into a water gun and shoot other people in the eyes.
 
Twitter
Eva J. Mah
‏@evajmah
I like that ! ~ RT @screamingeagle1 “When life gives you lemons, squirt someone in the eye.” — Cathy Guisewite (Hilarious! - Robert)
1:50 PM - 24 Jan 2009
 
Google Books
The Little Book of Humorous Quotes
Edited by Malcolm Kushner
The Little Quote Books (littlequotebooks.com)
2011
Pg. 22:
When life gives you lemons, squirt someone in the eye.
—Cathy Guisewite
 
Google Books
The 2,548 Wittiest Things Anybody Ever Said
By Robert Byrne
New York, NY: Touchstone
2012
Pg. ?:
813
If life gives you lemons, squirt the juice in people’s eyes. —Leo Roberts