The emergence of 'Mickey Mouse organization' as an insult
The very earliest instances of "Mickey Mouse organization [or operation or outfit]" that show up in Google Books search results are from the early 1930s and refer to the original Mickey Mouse organization—the Mickey Mouse Club. The term is not applied pejoratively. From "Louis Orlove Pays Special Attention to Kiddie Trailers," in Motion Picture Herald (1932) [combined snippets]:
Ever since Louis Orlove, manager of the Uptown Theatre, Milwaukee, was waylaid, bound, gagged and returned to his theatre by the business men and kiddies of his neighborhood, as a last minute means to prevent his migratory move to take over a more lucrative job at Detroit, Mich., he has been extremely busy setting in motion other schemes to keep the name of Uptown on the map and has apparently adjusted himself to what appears a life-long sentence in the city that was once, and maybe still is, famous for its Pilsener.
Among other important matters he has been paying special attention to "trailer language" in connection with his popular Mickey Mouse Club. The value of the personal touch in these advertisements was appraised by the home office of the Mickey Mouse organization, whose official bulletin recently reprinted some of Orlove's copy as an example of what to shoot at. It follows: “Big Hallowe'en Party—Saturday, October 31st—Tell Mother You Will Be—Home Late 'Cause Our—Show Is 'Ceptionally—Long!—Apple On The String Contest—Vodvil Acts! Nuff Sed!—You're Comin' Aintcha?"
And from "Heads Cascade Ginger Ale Sales" in Printer's Ink (1933) [combined snippets]:
Patrick H. Northchild has been appointed sales manager of the Monarch Manufacturing Company, Atlanta, Cascade Ginger Ale. He succeeds J. B. Whitton, who is now with the Mickey Mouse organization.
But instances where "Mickey Mouse" has acquired a pejorative tone begin appearing in the late 1950s. The first that a Google Books search finds is from a pseudo-letter dated December 22, 1956, in The MATS [Military Air Transport Service] Flyer, volume 4 (1957) [combined snippets]:
Dear Myrtle:
...
Remember my telling you that they were going to have an investigation and a board for the accident? Well, what a Mickey Mouse operation. It started out a couple of days after the accident, the 12th, I believe. They had the entire crew in for interrogation all day on the 11th, and that was when they took our statements.
From Neill Arrow, Painted Ocean (1962) [snippet]:
'What a mickey mouse outfit . . . did you stay long?'
'Only three months . . . got thrown out for bopping a flim.'
'A what?'
'Flim, you know, peculiar guy.'
From California Farmer, volume 225 (1966) [combined snippets]:
One of our least favorite organizations is the National Association of Water and Soil Conservation Districts. This Mickey Mouse outfit is trying to take over the whole world. They occupy vast areas of waste and duplication.
From "Muggsy," in Saturday Review (1967):
He [Muggsy Spanier] drank a lot, he ran around a lot; but, mostly, he played a lot. He made recordings with many bands under many different names, none of which his widow can recall today. Some of the bands were those of Sig Meyers, Charlie Straight, Elmer Schoebel, and Ray Miller. He was the lead horn player with The Bucktown Five, and for nearly seven years was with Ted Lewis. All of us who loved jazz always were wondering what this man was doing with that Mickey Mouse organization. Muggsy's explanation, when I asked him that question years later, was: "A gig is a gig."
And from Better Roads, volume 37 (1967) [combined snippets]:
Good and poor examples are usually spliced back to back on the film to get the message across. Poor traffic control, commonly referred to as a "Mickey Mouse" operation, is shown first. It is followed by additional footage to show how much more effective and practical it is to do it right. The men often get some good laughs watching a poor set-up, and they learn from watching how it should be done.
'Mickey Mouse' in slang dictionaries
The term Mickey Mouse as an adjective phrase has a more colorful and varied history in slang dictionaries than I had imagined. From Harold Wentworth & Stuart Flexner, Dictionary of American Slang, first edition (1960):
mickey mouse, mickey-mouse, micky mouse, micky-mouse adj. Sentimental insincere, or characterized by trick effects; said of pop. dance music or the musicians who play it. 1956: "A mickey-mouse band is a real corny outfit that pushes trombone sounds and uses out-of-tune saxes." S. Longstreet, The Real Jazz Old and New, 149. Musician use.
Mickey Mouse (movie) A documentary or short movie vividly showing the means of prevention, the causes, development, and care of venereal diseases; a documentary or short movie vividly showing methods of hand-to-hand combat. Wide W.W.II Army use, in ref. to such movies shown as part of soldiers' training courses.
Additional definitions listed in Harold Wentworth & Stuart Flexner, Dictionary of American Slang, second supplemented edition (1975):
Mickey Mouse, mickey mouse 1 Cheap, shoddy, or inferior; unfair, confused, or senseless; mean or "lousy." 2 Simple; easy; childlike. 1958: "At Michigan State [University] ... a 'Mickey Mouse course' mans a 'snap course.'" M[aurice] Crane, "Vox Bop" [American Speech, October 1958] 3 Foolish; inconsequential. Mainly student use. 4 An easy task; specif. an easy course in college, one that is of slight educational value and almost impossible to fail; "crib," "gut," "pipe." Student use. 5 Action, behavior, etc., that is unnecessary, cowardly, confused, etc.; a mistake. 1965: "Logistically so far, the only big Mickey Mouse ... was a brief shortage of ... jungle boots. ..." Time, Dec. 10, 33/34. Mainly Armed Forces use. 6 {derog.} A white person. Negro use. 7 To waste time ; fool around. 1973: "And the commissioner warns, 'We can't Mickey Mouse around while faced with technical challenges from other countries.'" R.G. Hummerstone, Fortune, May, 264.
That is a remarkable profusion of new meanings in less than two decades, including three new meanings as an adjective, three new meanings as a noun, and one new meaning as a noun. The areas of use are diverse, too, expanding from the original "Musician use" and "W.W.II Army use" of the 1930s and 1940s, to include "Mainly student use," "Student use," "Mainly Armed Forces use," and "Negro use" for some specialized definitions, and general population use for others.
'Mickey mouse' as a pejorative term in music
Crane's 1958 "Vox Bop" article (cited in Wentworth & Flexner, second edition, above), as quoted in Garry Apgar, A Mickey Mouse Reader (2014) discusses the term's evolution at some length:
Incidentally, a mickey or Mickey Mouse band is not merely a 'pop tune' band, as [Robert] Gold indicated [in a December 1957 article in American Speech titled "The Vernacular of the Jazz World"], but the kind of pop band that sounds as if it is playing background for an animated cartoon. Listen to Lawrence Welk, if you will, and discover how apt the expression is. (The term, which has been around almost as long as Mickey Mouse himself, has also come into common parlance in another sense at Michigan State [University], where a 'Mickey Mouse course' mans a snap course, or what Princeton undergraduates in my day called a gut course.
An editor's note following the excerpt from Crane observes that "Mickey Mouse music" was "an expression long used in Hollywood to describe the harmonized union of screen action with song and sound effects innovated by [Walt] Disney." The note then proceeds to the pejorative sense of the term:
As a term for "uncool" music, "Mickey Mouse" appeared in the first lexicon of jazz slang ["The 'Slanguage' of Swing—Terms the 'Cats' Use," in Down Beat magazine], authored by Carl Cons (Nov. 1935).
Unfortunately I can't find a copy of Cons's lexicon of jazz slang, so I don't know the wording of the "Mickey Mouse" entry.
In "Krupa Admits, 'I Can't Hit Long Ball Anymore," published in 1972 in International Association of Jazz Record Collectors Journal, the reporter interviewing jazz/big-band drummer Gene Krupa includes the following comment:
Mickey Mouse music in Krupa's day "was very syrupy, saccharin music exemplified by the [Guy] Lombardo bands."
Conclusions
The earliest insult terms that incorporated "Mickey Mouse" appear to have been the phrases "Mickey Mouse music" and "Mickey Mouse band," which jazz musicians in the 1930s used as a derisive way of referring to music that was too bland and characterless to suit their tastes. A glossary of jazz slang that appeared in the November 1935 issue of Down Beat magazine included some form of this insult, though I haven't been able to find a copy of it.
In World War II, servicemen in the U.S. Army used "Mickey Mouse movie" as an sardonic term for the informational films on venereal disease and the training films on hand-to-hand combat that all recruits were shown. By the late 1950s, "Mickey Mouse" was appearing as an adjective phrase in longer phrases such as "Mickey Mouse operation" with the denigrating sense of "low-quality, amateurish, or inferior."
From there the adjective phrase radiated in numerous directions, perhaps influenced by The Mickey Mouse Club TV show, which aired originally between 1955 and 1959, and in reruns through much of the 1960s—and eventually became synonymous (in the United States) with a kind of gee-whiz youthful wholesomeness that many young people in the 1960s and afterward considered an absurd fantasy for squares.
Though it would be reckless to attribute the popularity of "Mickey Mouse" as a negative adjective in recent decades entirely to the early pejorative 1930s jazz slang usage, I suspect that this early usage had a significant influence on subsequent developments in that direction.
