knock people's heads together

knock (people's) heads together

To forcefully make two or more people act, behave, or think in way that is appropriate or necessary. We're so far behind because your team keeps procrastinating. You need to go in there and knock their heads together. She claimed she would go into the negotiations and knock everyone's heads together until a deal was reached.
See also: head, knock, together

knock your/their/our heads together

To scold two or more people harshly. If you two do something this stupid again, I'm going to knock your heads together!
See also: head, knock, together
Farlex Dictionary of Idioms.

knock people's heads together

or

bang people's heads together

mainly BRITISH, INFORMAL
If you knock people's heads together or bang their heads together, you forcefully make them stop arguing. If he's unable to knock everybody's heads together, then questions are going to be raised about his own ability to continue in office. The idea is to bang their heads together until they come out with a sensible deal. Note: You can also say that someone bangs heads together or knocks heads together. Chris Smith said he would bang heads together.
See also: head, knock, together
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • bang (people's) heads together
  • bang people's heads together
  • bang your/their/our heads together
  • knock (people's) heads together
  • knock your/their/our heads together
  • lay down the law
  • lay down the law, to
  • protest too much
  • tear loose from (someone or something)
  • jam together