“When you leave New York, you are astonished at how clean the rest of the world is,” New York-based author Fran Lebowitz told People magazine in September 1978. “Clean is not enough.”
 
New York City would become cleaner after the 1970s. The Lebowitz line has been frequently cited.
 
   
Wikipedia: Fran Lebowitz
Frances Ann “Fran” Lebowitz (born October 27, 1950) is an American author and public speaker. Lebowitz is known for her sardonic social commentary on American life as filtered through her New York City sensibilities. Some reviewers have called her a modern-day Dorothy Parker.
     
People magazine
Fran Lebowitz Is New York’s Answer to Erma Bombeck: the Bette Midler of Belles Lettres
BY MARY VESPA UPDATED 09/04/1978 AT 01:00 AM EDT • ORIGINALLY PUBLISHED 09/04/1978 AT 01:00 AM EDT
(...)
Never prodigious, and wary of overexposure, she has committed herself only to a second book, tentatively titled Social Studies, for a six-figure advance. Will it be more universal and less New Yorky than her first work? “When you leave New York, you are astonished at how clean the rest of the world is,” marvels Lebowitz. Then she adds characteristically: “Clean is not enough.”
 
Google News Archive
7 December 1978, The Blade (Toledo, OH), Liz Smith gossip column, pg. P-5, col. 1:
“WHEN YOU LEAVE New York, you are astonished at how clean the rest of the world is,” marveled Fran Lebowitz in a People interview. She continues: “Clean is not enough.”
   
Google Books
Forbes Magazine
October 12, 1992
Pg. 264:
When you leave New York, you are astonished at how clean the rest of the world is. Clean is not enough. -FRAN LEBOWITZ
   
Google Books
America in Quotations
By Bahman Dehgan
Jefferson, NC: McFarland & Company, Inc.
2003
Pg. 46:
When you leave New York, you are astonished at how clean the rest of the world is. Clean is not enough.—Fran Lebowitz, 1946-
 
Google Books
The Little Red Book of New York Wisdom
Edited by Gregg Stebben and Jason Katzman
New York, NY: Skyhorse Publishing
2011
Pg. 88:
When you leave New York, you are astonished at how clean the rest of the world is. Clean is not enough.
FRAN LEBOWITZ
   
Twitter
Jewish Comedians
‏@JewishComedians
Fran Lebowitz: When you leave New York, you are astonished at how clean the rest of the world is. Clean is not enough.
7:23 PM - 15 Nov 2015