"A vegetarian is a person who doesn’t eat anything that can have children” is a popular line from American stand-up comedian David Brenner (1935-2014). The one-line saying has been cited in print since at least 1984.
Wikipedia: David Brenner
David Norris Brenner (February 4, 1936 – March 15, 2014) was an American stand-up comedian, actor and author. The most frequent guest on The Tonight Show Starring Johnny Carson in the 1970s and 80s, Brenner was a pioneer in the genre of observational comedy.
There’s Nothing Neat About Seeing Your Feet:
The Life & Times of a Fat American
By Ludlow Porch
Atlanta, GA: Peachtree Publishers
‘A vegetarian is a person who won’t eat anything that can have children.’ — David Brenner
13 May 1985, Cumberland (MD) Evening Times, Celebrity Cipher, pg. 19, col. 2:
PREVIOUS SOLUTION: “A vegetarian is a person who won’t eat anything that can have children.”—David Brenner.
9 January 1993, The Daily News (Huntingdon, PA), Daily Cryptoquotes, pg. 17, col. 1:
Yesterday’s Cryptoquote: A VEGETARIAN IS A PERSON WHO WON’T EAT ANYTHING THAT CAN HAVE CHILDREN.—DAVID BRENNER
The 2,548 Best Things Anybody Ever Said
By Robert Byrne
New York, NY: Fireside
A vegetarian is a person who won’t eat anything that can have children. —David Brenner
Fantabulous Quotes of Wisdom
By Romeo Marrishaw
Xlibris Corp. (Xlibris.com)
A vegetarian is a person who doesn’t eat anything that can have children.