It won't wash!

it won't wash

Something will not be accepted or believed as true. That kind of excuse may have worked in high school, but it won't wash with me. The deadline for the paper is tomorrow, no extensions. He may be able to skirt the issue in some regions, but it won't wash in these parts—these people want straight answers.
See also: wash
Farlex Dictionary of Idioms.

It won't wash!

Fig. Nobody will believe it! Sorry, it won't wash. Try another approach. Don't expect me to believe that! It won't wash.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • it won't wash
  • does not wash
  • use (someone or something) as an excuse (for something)
  • use as an excuse
  • excuse (one) for (something)
  • excuse for
  • ladies first
  • excusat
  • ignorantia
  • ignorantia juris non excusat