The phrase When pigs fly! is an adynaton—a figure of speech so hyperbolic that it describes an impossibility.
When I was growing up, When pigs fly! was my mom’s way of saying “no.” The quirky way she said it took the edge off of her denial to my request. And trust me, it was always for my own good.
- Miscarriage of justice
What When pigs fly! example would you add?