be not the done thing

be not the done thing

Of a given behavior, to be unacceptable, inappropriate, or incorrect in a particular social situation. Primarily heard in UK. You should know better than to wear a skirt like that to a formal dinner; it is simply not the done thing! I'm so glad smoking indoors is not the done thing anymore!
See also: done, not, thing
Farlex Dictionary of Idioms.
See also:
  • not done
  • cross the line
  • arsis
  • arsy
  • arsy-varsy
  • arsy-versy
  • up the booay
  • discretion
  • an ounce of discretion is worth a pound of wit