Literally, it simply refers to any living organism that munches cock in any form. Since introduced by teenagers in the late 2010s, it can have a wide variety of meanings, virtually anything you desire while considering the level of offense you wish it to have. It can also be used as a conversation initiator. assholedickfucktittyfuck my assGood dayhelloSuperbMy dick hurts
(Silence) Person 1:Cockmuncher? Person 2:Cockmuncher!!
1: Have you seen my dildos? 2. Shut up you fucking cockmuncher.