stick the knife in

put the knife in

To be, do, or say something especially critical, unpleasant, or mean-spirited, especially to someone who is already vulnerable or weak. Primarily heard in UK. John seems genuinely remorseful for what happened; there doesn't seem to be any reason to put the knife in at this point. And then he really put the knife in by telling me that he'd only pretended to like my writing. You would think the rise of cheap electric cars would put the knockers on Big Oil's profits, but they actually seem to be embracing the change.
See also: knife, put

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
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.