Cockamamie/cockamamey

American slang for ridiculous or implausible as in a cockamamie idea is first attested from the 1930s but its origin remains unknown. Etymological attempts to link it to a mispronunciation of decalcomania, a craze or mania for decals or transfers that started in France in the mid-19th century and then spread to America are interesting but highly improbable and far from proven.