Meaning useless, damaged or lazy. When someone is a Munt, they are useless at jobs and minor tasks that are in everyday life. When you are to Munt something, you would have destroyed it.
Eg 1.
Andrew: “My co-worker at the cleaning company doesn’t even clean the mop bucket out when he uses it, nor does he clean the toilets properly! He is a munt!”
Eg 2.
Belinda “Now be careful with my favourite doll! Don’t munt it!”
To munt someone, you and a friend must have a dead body, preferably a couple days old, and one of you fucks it while the other jumps on the stomach and pushes the guts out onto your cock.