cartoon mouse character created 1928 by U.S. animator Walt Disney (1901-1966). As an adjective meaning "small and worthless" it dates 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.
To treat someone shabbily; ill-use someone; screw, shaft: ''I think we got Mickey Moused,'' Williams said. ''My best pitcher is washed right down the drain, and I don't like it'' (1980s+)
[apparently this pejorative trend began after the wide distribution of cheap Mickey Mouse wrist watches, showing the cartoon character on the face, with his arms as the watch's hands, which were regarded as shoddy, gimmicky, etc, at that time; the diminutive rodent continues to be extremely popular with children]