La farce du jour

(un) contrepet or (une) contrepèterie = a (deliberate) spoonerism, where one or more syllables are deliberately inverted to make another sentence. It's definitely an art de vivre, as illustrated by the famous column titled "Sur l'Album de la Comtesse" in French newspaper Le canard enchaîné, that delights its readers with contrepèteries related to the latest news. And, as there's nothing like a few examples to grab the concept, here we go:
Le mot de guichet (word of the counter) -> Le godemiché (see here)
Les mots grecs (greek words) -> Les gros mecs (big guys)
Les proues qui tuent (killing prows) -> Les trous qui puent (stinking holes)

Obviously, a contrepèterie doesn't have to make any sense at all, or be subtle for that matter: 90% of them use slang sexual references, but isn't that half of the fun.