Do you have an interesting idiom?

By definition, an idiom is figurative; its meaning is different from the combination of individual words making up the phrase. One of my favorites is something my mother used to say, referring to someone who was extremely civil in tongue, never cursed:

“He wouldn’t say shit if he had a mouthful!”

Let’s get a collection of them. And, for the benefit of any jellies who have a first language other than English, let’s also give the actual meaning of the phrase.