A poor person who acts different is said to be “crazy,” but a rich person who acts different is merely “eccentric”—a small personality quirk. The book Majority of One (1957), by Sydney J. Harris, stated the difference between “eccentric” and “crazy”:
 
There is an old English saying to the effect that “a poor man is crazy, but a rich man is just ‘eccentric.’”
 
It’s not known how old the saying is, but it’s been repeated often since the mid-1900s. “It’s an ancient maxim, of course, that poor people are called crazy. The rich are merely eccentric” was cited in print in 1979.
 
   
Google Books
Majority of One
By Sydney J. Harris
Boston, MA: Houghton Mifflin
1957
Pg. 6:
There is an old English saying to the effect that “a poor man is crazy, but a rich man is just ‘eccentric.’”
 
Google News Archive
5 August 1971, Milwaukee (WI) Journal, “Don’t Poor Mouth Hope ‘Cause He’s Rich” by Burt Prelutsky (Los Angeles Times Service), GreenSheet, pg. 1, col. 2:
Poor people are crazy, Only the wealthy can afford to be eccentric.
 
Google Books
Teaching Elementary Social Studies:
A New Perspective
By Gene Edward Rooze and Leona Mitchell Foerster
Columbus, OH: Merrill
1972
Pg. 303:
Perhaps you have heard the old saying that if you’re rich and “different” you’re called “eccentric”; if you’re poor and “different,” you’re just plain crazy.
 
Google Books
The Westing Game
By Ellen Raskin
New York, NY: Dutton
1978
Pg. 31:
“The poor are crazy, the rich just eccentric,” Mr. Hoo said bitterly.
 
18 February 1979, Chronicle-Telegram (Elyria, OH), “Rod gets his now” by Melvin Durslag, pg. C-2, col. 1:
It’s an ancient maxim, of course, that poor people are called crazy. The rich are merely eccentric.
   
Google Books
5 October 1981, New York magazine, Letters, pg. 10, col. 2:
“FRAN LEBOWITZ ISN’T KIDDING” [BY Cynthia Heimel, September 14] brought to mind an old adage: “A poor person who acts unusual is labeled as crazy; a rich person who acts the same way is called an eccentric.” Someday I hope to be an eccentric.
David K. Miller
Manhattan
 
Google Books
Point Blank
By Jack Hild
New York, NY: Worldwide
1987
Pg. 24:
Rich people were eccentric. Poor people could only afford to be crazy.
   
Google Books
Beauty is the Beast:
Appearance-impaired Children in America
By Ann H. Beuf
Philadelphia, PA: University of Pennsylvania Press
1990
Pg. 15:
This concept is illustrated by the saying, “Poor people are crazy, but rich people are eccentric.”
 
Google Books
Three Complete Novels
By Lawrence Sanders
New York, NY: G.P. Putnam’s Sons
1998
Pg. 428:
I remembered the old saw: “The poor are crazy; the rich are eccentric.”
 
Twitter
tilton fenwick
‏@tiltonfenwick  
“Crazy people are only crazy when they are poor. When they are rich, they are eccentric!” @MARYMCDONALDINC #milliondollardecorators
7:23 PM - 8 Jan 13