you know who/what

you know what

1. A phrase used to convey a realization, often mid-sentence. I wasn't going to go out with you guys tonight, but hey, you know what, I'm in!
2. A rhetorical question posed before a statement one considers to be the blunt truth, often during an argument or heated exchange. You know what, John? I think you never really loved me.
3. A statement asserting that the person to whom one is speaking does in fact know something that they claim not to. A: "What is the matter with you?" B: "You know what!"
See also: know, what
Farlex Dictionary of Idioms.

you know ˈwho/ˈwhat

(spoken) used to refer to somebody/something without mentioning a name: I saw you know who this morning. She didn’t even say hello to me.
See also: know, what, who
Farlex Partner Idioms Dictionary
See also:
  • you know what
  • break the bank
  • break the bank, to
  • come to think of it
  • count for
  • count for (something)
  • be (not) the marrying kind
  • be (not) as black as (someone or something) is painted
  • be (not) all beer and skittles
  • come with (someone or something)