The story
From Mickey, a diminutive of the given name Michael, + mouse, referring to the species of the character. Walt Disney chose the name Mickey Mouse in 1928, changing it from Mortimer Mouse at the suggestion of his wife, Lillian, who felt the original name was too formal for the character's playful nature. The derogatory adjectival sense developed in the US after WWII, originally applied to dance music, then broadened.
Etymology from Wiktionary, CC BY-SA 4.0.