in a pig’s eye

Never! Several sources have been suggested for this Amer- icanism from the late nineteenth century. One holds that it is rhyming slang for “when pigs fly,” which of course is never. Another, more probable theory is that it is a euphemism for “in a pig’s ass,” which came from a bawdy song. Whatever the true origin, it has been on its way to becoming a cliché since about 1950.