Green’s Dictionary of Slang

(US) dirty, filthy.

1968		T. Wolfe Electric Kool-Aid Acid Test (1969) 24: It looks like he has on about eight pairs of clown’s pants [...] each one filthier than the next one, all black, sooty, torn, mungey and fungous.
1971		E.E. Landy Underground Dict. (1972) 136: mungy [...] the state and feeling of having a very oily face when one is on an acid (LSD) trip.