not cool!

not cool!

A set phrase said in response to something that is considered unacceptable, inappropriate, or mean-spirited. A: "So then I pulled the chair out from under him just as he was about to sit down!" B: "Not cool, dude. You could have really hurt him!" A: "She said she was going to dock my pay because of what happened." B: "Wow, not cool!"
See also: not
Farlex Dictionary of Idioms.
See also:
  • if you don't have anything nice to say, don't say anything at all
  • knives
  • get (one's)/the knife into (someone)
  • get the knife into someone
  • get your knife into somebody
  • put the knife in
  • put/stick the knife in
  • stick the knife in
  • make life difficult
  • make life difficult (for one)