“All mushrooms are edible, some only once” is a saying that has been printed on many images. Authorship is unknown.
 
“All mushrooms are edible. Of course there are some you’ll eat only once” was published in an Olympia, Washington, newspaper in 1944. “All mushrooms are edible, some only once” was published in a Ukiah, California, newspaper in 1980 and 1981.
 
             
19 March 1944, The Sunday Olympian (Olympia, WA), “Olive Barber writes,” pg. 4, col. 6:
All mushrooms are edible. Of course there are some you’ll eat only once. After that you’ll be so busy playing a harp and keeping your wings on straight, you won’t have time for mushroom eating.
   
12 November 1980. Ukiah (CA) Daily Journal, “College of Redwoods offers Mushroom fair,” pg. 21, col. 5:
“All mushrooms are edible, some only once,” was the announcement made to introduce the public to the Mushroom Fair to be held Sunday in the Spruce Street classrooms of the Mendocino Branch of College of the Redwoods, next door to the Building Department offices, in Fort Bragg.
   
13 November 1981. Ukiah (CA) Daily Journal, “Mushroom fair Sunday,” pg. 10, col. 5:
“All mushrooms are edible, some only once,” says Teresa Sholars, instructor at the Mendocino Coast Educational Center for the College of the Redwoods.
 
10 November 1985, The Press Democrat (Santa Rosa, CA), “Mushroom display is today,” pg. 3G, col. 3:
The fair offers a way to learn which mushrooms you may wish to take home for dinner, bearing this thought in mind: “All mushrooms are edible—some only once.”
   
Google Books
Handbook of Mushroom Poisoning:
Diagnosis and Treatment
By Barry H. Rumack and David G. Spoerke
Baco Raton, FL: CRC Press
1994
Pg. 10:
The gentleman was present when a woman brought her mushrooms in and asked the oft repeated “Is this edible?” The reply by the official was, “Madame, all mushrooms are edible—some only once.”
 
22 March 1995, Fort Worth (TX) Star-Telegram, “Mushrooms cap a good meal” by Ann Steiner and Cici Williamson, pg. 8:
“All mushrooms are edible - some, only once!” quips Dr. Livia Rev-Kury, owner of The Cafe Budapest in Boston.
   
Google Groups: rec.arts.disney
The DEFINITIVE Indy Ride Review (Final Version
Robert Anderson
5/1/95
(...)
“All mushrooms are edible - but some only once.”
 
Twitter
Marko Kloos
@markokloos
Favorite line remembered from my Army survival training: “All mushrooms are edible—some only once.”
9:10 AM - 13 Jan 2009
   
Twitter
GreenModernKits
@greenmodernkits
“All mushrooms are edible; but some only once.” ~Croatian proverb
9:07 AM - 11 Apr 2009
   
Reddit—Quotes
“All mushrooms are edible ... some only once.”—multiple attributions (self.quotes)
submitted May 10, 2015 by photolouis
   
Reddit—Shower Thoughts
All mushrooms are edible: some just once.
submitted July 21, 2015 by PeraCotta
   
Reddit—Shower Thoughts
All mushrooms are edible, some only once.
submitted December 6, 2017 by lo-lux
 
Reddit—Jokes
All mushrooms are edible
submitted April 16, 2018 by maxofJupiter1
But some mushrooms are only edible once