The noun daffynition designates a humorous redefinition of an existing word or phrase, presented as a dictionary definition.

This noun occurs, for example, in Council on Aging—Ava Senior Center, by Tommy Robertson, published in the Douglas County Herald (Ava, Missouri, USA) of Thursday 23^rd April 2020 [page B-Four, column 6]:

From my Mom’s Bible: God is crazy about you—He sends you flowers every spring. He sends you a sunrise every morning.
Daffynition of camping: Where you spend a small fortune to live like a homeless person.

Of American-English origin, the noun daffynition is a blend of:
– the adjective daffy, meaning daft, silly;
– the noun definition, in the sense of a formal and concise statement of the meaning of a word or phrase, especially in a dictionary.

The earliest occurrences of the noun daffynition that I have found are as follows, in chronological order:

1 & 2-: From the weekly satirical magazine Judge (New York City: Leslie-Judge Company):

1-: Of Saturday 24^th September 1910 [Vol. 59, No. 1510, page 9, column 2]:

Daffynitions.

TIGHT-ROPE walker—A person who has a steady job.
Awning maker—A man whose purpose in life is to put other businesses in the shade, and does.
Baseball—A game which is not as bad as its name suggests.
Bigamy—An over-issue of matrimonial bonds.
Carriage wheel—A part of a carriage which does not begin to work until it is tired.
Coal dealers—A class of business men who lie in weight for you.
Colleges—Institutions of learning that always retain their faculties.
Dead letter—A letter that died at its post.
Dentist—About the only man who lives from hand to mouth and always looks prosperous.
Fame—An elevation to which people are placed so that the public may get a better chance to throw mud at them.
Fire engine—A water pitcher.
Fly fishing—Reel sport.
Hansom—A vehicle that is anything but handsome.

2-: Of Saturday 1^st October 1910 [Vol. 59, No. 1511, page 7, columns 2 & 3]:

Daffynitions.

ANTI-FAT DOCTOR—A physician who lives off the fat of the land.
Iron—That ingredient found in determined people’s blood. (That found in stubborn people is called “pig iron.”)
Lawyer—A professional man who is strongest when fee-blest.
Oarsman—A man who gets there by going backward.
Publisher (of a comic paper)—One who has his wits about him.
River beds—The bottom of the river. So called because it has springs and is covered with sheets of water.
Red—A danger signal on railroads, water, men’s noses, and women’s cheeks.
Silence—About the only thing which, when it falls, isn’t broken.

Note: Perhaps in relation to its own daffynitions, Judge published the following on Saturday 1^st October 1910 [page 4, column 1]:

Dictionary Humor.

JUDGE has long known that of the making of jokes there seemed to be no end. The source of inspiration is out at last. A writer in the Boston Transcript says that one may, “by taking the dictionary page by page and examining each word for its humorous possibilities, make as high as twenty jokes an hour from a single page of the dictionary if one has a practical working knowledge of the characteristics of marketable humor.”
This is good news. Judge has worried a good deal about the joke supply. The alarm, however, has been false. The English language is not a dead one, but one very much alive. New words are added daily, and if the supply of such additions runs low, the various Joque Smiths—by long odds the largest family of Smiths in the United States—can be depended upon to increase the supply.
Let the dictionary now take its place by the side of Joe Miller’s Joke Book. In the future, will contributors please specify the dictionary used, whether “Webster’s,” “Standard,” “Century,” “New Home,” “Sweet Briar,” or whatnot? By so doing, the editor of Judge may be able to understand some jokes which otherwise would never be appreciated.

3-: From an account of a show given by the pupils of the Steilacoom primary schools, published in The Tacoma Daily Ledger (Tacoma, Washington, USA) of Thursday 15^th June 1911 [Vol. 29, No. 71, page 7 (erroneously dated Wednesday 14^th June 1911), column 2]:

Ida Bradley delivered Adelaide Proctor’s poem, “Words,” with good effect. The “Class in Daffynitions” was humorous and received its share of applause.
[…]
The program follows:
[…]
Class in daffynitions, grammar and intermediate pupils.

4-: From Hanford Union High School News, published in the Hanford Morning Journal (Hanford, California, USA) of Thursday 30^th March 1922 [30^th Year, No. 73, page 6, column 2]:

H. U. H. S. DAFFYNITIONS

Books—something for the girl’s escorts to carry home.
Buzzers—a periodic interruption of intellectual toil???
Chewing Gum—the only work some pupils ever accomplish are mouth calisthenics.
Chow Wagon—a moving cafeteria.
Clocks—the only things in the schools that make use of the precious minutes.
Examinations—when the teacher racks his brain and the student shows he has none.
Fountain Pens—things our fond parents buy for others to use—and lose.
Garbage Cans—things some pupils do not know exist.
Lawns—something that is yet to be.
Library—a place where we can gaze out of the windows in peace.
Latin Composition—that which put the “row” in sorrow.
Mirrors—reflections of the school’s intelligence.
Old Gym—as much like the one we ought to have as a donkey cart is like a Packard.
Shades—on which excess of brilliant knowledge is expended.
Telephones—the silent communicators of nothing.
Yard—exercising grounds for gymnasium, horses and wagons.