stick the knife in

stick the knife in

To be, do, or say something especially critical, unpleasant, or mean-spirited, especially to someone who is already vulnerable or weak. John seems genuinely remorseful for what happened. There doesn't seem to be any reason to stick the knife in at this point. And then he really stuck the knife in by telling me that he'd only pretended to like my writing.
See also: knife, stick
Farlex Dictionary of Idioms.

put/stick the ˈknife in

,

put/stick the ˈknife into somebody

(informal) criticize somebody or deliberately try to harm them: The senator has quite a few enemies that would love to stick the knife in if they got the chance.
See also: knife, put, stick
Farlex Partner Idioms Dictionary
See also:
  • get (one's)/the knife into (someone)
  • get the knife into someone
  • get your knife into somebody
  • knives
  • put the knife in
  • put/stick the knife in
  • the jaws of (something)
  • the jaws of death, defeat, etc.
  • taco stand
  • rumble on
References in periodicals archive
She told me she needs it because she was raped by a boy on her way back from school and if she ever sees him again she says she is going to stick the knife in him.
I know knives are bad and I want to tell someone but if she know I grassed, she might stick the knife in me instead.
MUST involve the adults