As far as I can tell, cockamamie is not from Yiddish, but rather
a child's corruption of decalcomania, the cheap and temporary
tattoos. " dye transfers that youngsters used to put on their hands
and arms. Since they were cheap, they soon wore off. So,
'cockamamie' first meant anything trifling or second-rate, and
later came to mean simply silly or laughable." From "Morris
Dictionary of Word and Phrase Origins" by William and Mary Morris
(HarperCollins, New York, 1977, 1988).