Green’s Dictionary of Slang

(US campus) filth or dirt of any kind, anything disgusting.

1949		J.H. Burns Lucifer with a Book 186: Pass the Mung, Paganini, an upperformer said. – There’s Mung in the cauliflower, another said. Mung. That was the Academy’s name for the food they ate.
1962		J. Quirk No Red Ribbons (1968) 89: You don‘t have to build things, either, like churches and all that mung. [Ibid.] 176: Whiskey Jack said into his mike, ‘Fighter bombers eat mung!’.
1975		L. Bangs in Psychotic Reactions (1988) 174: It was like the physical externalization of all that fat and mung Lou must have lost when he shot those vitamins.
1989		P. Munro Sl. U.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: mung n. A particularly runny type of arse feta (qv).
2001		OnLine Dict. of Playground Sl. 🌐 mung n. (1) Used quite frequently back in the 1950’s. Puported to be the nastiest substance on earth consisting of a mixture of assorted bodily fluids and solids together with fetid pus from a dead man’s ear.