bang (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 bang their heads together. She claimed she would go into the negotiations and bang everyone's heads together until a deal was reached.
bang your/their/our heads together
To scold two or more people harshly. If you two do something this stupid again, I'm going to bang your heads together!
bang (or knock) people's heads together
reprimand people severely, especially in an attempt to stop them arguing. 1998 Community Care There are few signs yet that the SEU has been willing to bang government heads together over social security policy.