Green’s Dictionary of Slang

mung v.4

[mong (out) v.]

(S.Afr.) to render passive.

[SA]Mail & Guardian (Johannesburg) 24 Sept. 🌐 This [i.e. cannabis] not the drug we associate with violence [...] If anything this shit is going to mung you out. It’ll blitzkrieg the fight right out of your balls.