“Shoes are required to eat in the cafeteria” is an old joke sign that supposedly appeared in a college cafeteria in 1975. Underneath the sign was scribbled, “Socks can eat any place they want.” The joke was popularized in a 1975 issue of The Reader’s Digest and has been included in many humor collections.
 
   
Google Books
The Reader’s Digest
Volume 106
1975
Pg. 42:
A notice in a University of Colorado campus cafeteria stated: “Shoes are required to eat in the cafeteria.”
 
Someone wrote below: “Socks can eat wherever they want.”
— Contributed by Mike Shrout
   
20 May 1975, Bennington (VT) Banner, pg. 4, col. 7:
Humor
Cafeteria rules
A notice in a University of Colorado campus cafeteria stated: “Shoes are required to eat in the cafeteria.”
 
Someone wrote below: “Socks can eat wherever they want.” 
—Reader’s Digest
 
1 December 1975, The Express (Lock Haven, PA), pg. 10, col. 2:
Watch that syntax!...Catholic Digest’s Kenn Maloney tells about the sign at Georgetown University which reads: “Shoes Are Required to Eat in the Cafeteria.”...Underneath, someone scribbled: “Socks May Eat Where They Want To.”
     
6 June 1976, The Sun (Baltimore, MD), pg. SM30: 
Sign in a university cafeteria: “Shoes are required to eat in the cafeteria.” Someone wrote below: “Slacks can eat wherever they want.”
 
Google News Archive
22 November 1976, Prescott (AZ) Courier, “Quips & Quotes,” Magazine, pg. ?, col. 2:
A sign on a university bulletin board reads: “Shoes Are Required to Eat in the Cafeteria.”
Underneath, somebody had scribbled, “Socks may eat wherever they want to.”
—Dorothea Kent
 
Google Books
Fractured English
By Richard Lederer
New York, NY: Pocket Books
1996
Pg. 81:
At the entrance of a college cafeteria: SHOES ARE REQUIRED TO EAT IN THE CAFETERIA. Penciled underneath: SOCKS CAN EAT ANYWHERE THEY WANT.
 
TheTrucker.com
Joke Of The Day
Say what?
The Trucker Staff
7/12/2009
(...)
Sign in a cafeteria: “Shoes are required to eat in the cafeteria. In pencil beneath the sign: Socks can eat anyplace they want.”
 
San Diego (CA) Union-Tribune
Give us this season just 2 more wins
Written by Tom Blair‎
4:04 a.m., Dec. 19, 2010
(...)
Evan Bostich, a veteran of the grammar police, wonders at the sign he saw posted outside a North County diner: “Shirts and shoes are required to eat inside.” “So why,” he asks, “can’t shoes and shirts eat outside?”