Is were you put a sandwich in a bag with any type of filling and slap someone round the face with it.
Oh my god is you dont shut up im gonna (sandwich slap) you
Self explanatory. Slapping someone in the face with a sandwich. The larger the sandwich, the better. Subs are preferred. For a cheap, tasty slap, head on over to Subway for a $5 foot long.
Girl: Look, that guy is eating a sub.
Guy: What an ass, I'm gonna go sandwich slap the shit out of him.