to "fiend" up money, drugs or alcohol. It can relate to other things but it ususally has something to do with crime.
Liam: man i was so fucked last night.
Adam: man you mungled the shit out them little kids last night.
Liam: shit rolls down hill.
Getting absolutely out of your mind, usually on ellicit substances or booze.
"Man, you look mungled"
"Well I have done 5 pills"