BBB Etymology - Hoist With His Own Petard

A "petard" was a medieval weapon, specifically a small bomb used to blow open the gates of a castle under siege. They sometimes malfunctioned, "hoisting" (blowing skyward) the "engineers" delegated to plant the devices.

An oft misquoted phrase from Shakespeare comes from Act III of "Hamlet". Hamlet, having sidestepped an assassination plot by having the unwitting bearers (Rosencrantz and Guildenstern) of the assassination order themselves "whacked", muses on the justice of the moment: "'Tis the sport to have the engineer hoist with his own petard." This metaphorical use of the phrase to mean "someone being ruined or destroyed by the very plans or weapons they intended to use on someone else" has remained popular .. my favorite modern example is the Coyote in the Roadrunner cartoons.