(transitive, simile) To have an extensive and penetrating understanding of (something or someone).

(idiomatic, vulgar) Synonym of I don't know

(usually in the past tense) To have known a famous person before he or she was famous.

(chiefly US, in negative constructions) To know something, even if only a little, about. / (chiefly US, idiomatic) To know nothing, or almost nothing, about.

Alternative form of know what is what

(idiomatic) To be experienced or well-informed. / (idiomatic) To be astute, perceptive enough to observe a situation that is not what it seems and recognize its true nature.

To be spoiled; to have an easy life without appreciating it.

The name of something the speaker does not want to mention, but which is known, or very likely to be known, to the listener. It can be plural (as in "... the you-know-whats").

(idiomatic) A phrase used to get someone's attention before announcing something.

(informal) I know; I am very familiar with it (some stated fact).