it/that won't do

it/that won't do

It/that is totally unacceptable or unsatisfactory. Primarily heard in UK. A: "It will probably be the end of next week before I'm finished with this project." B: "That simply won't do, Jenkins. I don't care how, but I want it finished by Monday morning!" I was going to tell them I couldn't come to dinner because of a prior engagement, but I knew that wouldn't do.
See also: that
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

it/that (just) won’t ˈdo

,

it/that will never ˈdo

(especially British English) used to say that a situation is not satisfactory and should be changed or improved: He’s spending every afternoon in the park with his friends instead of going to school, and that just won’t do!I feel very upset but it would never do to show it.
See also: that
Farlex Partner Idioms Dictionary © Farlex 2017
See also: