When an arguement gets violent.
Usually a beating of some kind, the mash being the victim and the bangers being their attackers.
It doesn't literally make sense, since sausages don't usually beat down on mashed potato, but whatever.
Hey You!! Give us ya lunch money! Or there'll be a Bangers and Mash situation.... And you're the mash!!
Suck my Non Existent Penis. S my D for those who don't have a dick.
Guy: S my D
Girl: No, S my NEP
Jessi Slaughter: If you hate me, you know what... Suck my Non Existing Penis, okay? Just suck it.