get your knife into somebody

get (one's)/the knife into (someone)

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 get the knife into him at this point. And then he really got his knife into me by saying that he'd only pretended to like my writing.
See also: get, knife
Farlex Dictionary of Idioms.

get your ˈknife into somebody

,

have your ˈknife in somebody

(informal) harm and continue to harm somebody (usually not physically) whom you consider your enemy: He’s had his knife into me for months, and every time I make a mistake, he tells my boss.
See also: get, knife, somebody
Farlex Partner Idioms Dictionary
See also:
  • get (one's)/the knife into (someone)
  • get the knife into someone
  • knives
  • put the knife in
  • put/stick the knife in
  • stick the knife in
  • the jaws of (something)
  • the jaws of death, defeat, etc.
  • taco stand
  • rumble on