The French idiom “filer un mauvais coton” literally translates as “to spin a bad cotton”! But what it really means is “to wither away; to have deteriorating health; to do bad business; to lead a disorderly life leading to nothing; or to run wild.”

This saying dates back to the end of the 17th century. Then, it meant “to ruin oneself.” It was associated with the expression “jeter un vilain coton,” which meant “to throw an ugly cotton.” This in turn came from the tendency of cloth to lose balls of cotton thread as they gradually disintegrate.

The meaning of the expression changed by the 19th century to mean “to wither away from disease.” And the use of the word “vilain” meaning “ugly” was replaced by the word “mauvais,” meaning “bad.”

The other factor leading to the change in this saying was the introduction of cotton mills. In these mills, cotton was spun, so to “throw” cotton was replaced by “to spin” a bad cotton.

The closest English equivalents to this idiom are “to waste away” and “to be in a tight spot.”