and that's flat
And that is final; and the issue is settled or completed. Primarily heard in UK. You are going to your sister's recital and that's flat! No more complaining.
and that's flat!
old-fashioned And that (decision) is final! Look, I told you I'm moving to Canada after high school, and that's flat!
that's flat
used to indicate that you have reached a decision and will not be persuaded to change your mind. informaland ˌthat’s ˈflat!
(British English, spoken) that is my final decision and I will not change my mind: I’m not lending you any more money, and that’s flat!