An act similar to kissing, but far more brutal. It involves thrashing, intense tongue movement and head banging centred around the lip area. Usually done between romantically involved metal-heads during a brutal deathcore breakdown.
Person 1: What the hell was that? Im filing a domestic violence report!
Person 2: chillax ya turtle sphincter, we're just Lip Moshing.
Person 1: ohhhh, ok! Now i know!
*both high five while freeze frame jumping*