What is the history behind the phrase "a Mickey Mouse outfit" ? Where
does the saying come from or first originate? We all know the context
in which it is used today to mean a poor company, but what does that
have to do with Disney?

There is a lot of speculation, and even some informed-sounding
statements, on the Internet as to the origin of "Mickey Mouse" as a
derogative adjective.  Some think that it relates to the poor quality
of Mickey Mouse watches.  Another source traces it to American college
students of the late 1950s, who would describe an easy course as "a
Mickey Mouse course."  Yet another goes back to World War II, where
soldiers apparently referred to absurd army routine as "mickey mouse".

"Expressions and Sayings: M"
Scorpio Tales
http://users.tinyonline.co.uk/gswithenbank/sayingsm.htm

"Reflects Life"
Jeff Rice, Networked Writing Environment, University of Florida
http://web.nwe.ufl.edu/~jrice/1784/jwillis/life.html

"M-I-C-K-E-Y M-O-U-S-A", by Ellie Badesch (1999) 
Tomarken.com
http://www.tomarken.com/content/res/articles/2002/mickeymousa.shtml

But the true origin seems to be in the jazz world.  According to the
Online Etymology Dictionary (a source that I've found trustworthy in
the past):

"Mickey mouse (adj.) 'small and worthless' is from 1936, originally
used especially of mediocre dance-band music, a put-down based on the
type of tunes played as background in cartoon films ...."

"ETYMOLOGY Mi-Mn"
Online Etymology Dictionary
http://www.geocities.com/etymonline/m4etym.htm

For other references to this use, see:

"Jazz Glossary"
Michael Borshuk, Department of English, University of Alberta
http://www.ualberta.ca/~mborshuk/gloss.htm

"Swing Era and Modern Colloquialisms"
Big Bands Database Plus
http://64.33.34.112/.WWW/slang.html

This use came less than a decade after Mickey Mouse was created!

- justaskscott-ga


Search terms used on Google, in various combinations:

"mickey mouse"
"a mickey mouse"
etymology
slang
dictionary
idiom

Superb answer! The jazz music one makes extreme sense when you think
about it and the dates match up nicely as well. Thank you.

"Mickey Mouse" has officially entered the English lexicon!
http://www.bartleby.com/61/1/M0270100.html

From "Stewart’s Corner: Buzzwords" 
"Mickey Mouse 
This is an AE [American English] expression that means something is
simple or idiotic. Mickey Mouse is sometimes abbreviated to MM. When
somebody is said to be running a Mickey Mouse operation, it is a
negative term about a company, a government or the state of a national
economy."
http://www.ntnu.no/universitetsavisa/1398/stewart.html

I was fully aware of the meaning of the phrase as I stated - it was
the origin I was after.