cartoon mouse character created 1928 by U.S. animator Walt Disney (1901-1966). As an adjective meaning "small and worthless, petty, inconsequential" it was in use by 1951, perhaps from the popularity of the cheaply made Mickey Mouse wristwatch; it was used by 1935 in reference to mediocre dance-band music, based on the type of tunes played as background in cartoon films.
"peep show contained in a box," 1680s, so called "in imitation of the foreign way of pronouncing rare show" [Johnson]. "Johnson's statement is prob. correct; the early exhibitors of peep-shows appear to have been usually Savoyards, from whom the form was no doubt adopted" [OED]. Compare German raritäten-kabinet "cabinet of curiosities or rarities." Early peep shows were more innocent than what usually was meant later by that term.