From Longman Dictionary of Contemporary Englishbang/knock somebody’s heads togetherbang/knock somebody’s heads togetherspoken used to say that two people or groups should be forced to stop arguing and start to behave sensibly → head
Examples from the Corpus
bang/knock somebody’s heads together• He caught hold of the two nearest him and knocked their heads together, kicked two more and grabbed the ringleaders.• She'd just box a few ears, knock a few heads together like she did with the Rattries, and chase them off. 