The end nub of a Subway, Quizno's, Firehouse, or some other sub sandwich shop, sub (usually on the 12") that has no sort of meat or vegetable to be heard of, only a large amount of mustard, ranch, or some other sauce on the sandwich, that has somehow ventured down the sandwich, into the end. A sauce delta, if you will. Perhaps even a resevour tip for sauces.
A prime opportunity to regret wearing a white shirt, and getting mustard on your sandwich.
Man 1 - "Oh dude, what's happening with that sub there? Aren't you going to finish it?"
Man 2 - "Nah man, it's nothing but a saucewich, I'll just throw it away."
"SHIT! I dropped my saucewich on my fucking khakis! RUINED!"