Laisser pisser le mérinos

Literally: To let the merino piss

Example: “Inutile de t'énerver contre le patron ; laisse pisser le mérinos.” — No point getting worked up at the boss; let things ride.

English equivalent: To let things ride

Origin: The older form is laisser pisser la bête (let the animal piss), from the 19th century and from the men who drove teams. Draft animals will foul the road on the move, but relieving themselves while walking is another matter and risks trouble, so the driver stopped and waited — which meant being in no hurry, unbothered, content to let events happen. That is precisely the sense the phrase carries. The merino displaced the plain bête later, as a joke: the breed's wool was in vogue and the word was on everybody's lips. A story is also told about Louis XIV, whose flock of 366 merinos was installed at Rambouillet, one of which urinated on the royal foot, prompting the king to tell the flustered breeder to let it finish. No lexicographer cites it and it reaches print long after the expression does, so it looks invented afterwards.