Idiom: When Pigs Fly Posted on 15th November 201814th November 2018 by DoubleClick When Pigs Fly: express that something is highly unlikely ever to happen Example: My children asked me to go on a two month vacation. When pigs fly! Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Posted in Idiom and tagged Idiom W.