One theory holds that World War II U.S. Navy
Military Indoctrination Centers, Or M.I.C.s, where undisciplined sailors
were restrained, gave their initials to this expression for petty rules.
The expression has been around since early World War II and probably can
be explained by the fact that such rules seem silly and childish, like
Mickey Mouse cartoons. Mickey Mouse was better honored when his name
became the password chosen by intelligence officers in planning the
greatest invasion in the history of warfare - Normandy, 1944. Mickey Mouse
diagrams were maps made for plotting positions of convoys and bombarding
forces at Normandy.