Yes. I know its origin.

It evolved from a slang insult "munter", which was first coined in Northcote College in around 1985-86 by bored members of a German class. "Munter" means "gay" in German - in the sense of "bright, joyous". The students were looking for another slur to add to their already extensive and complex homophobic vocabulary. This was a rare opportunity to put their English-German dictionary to use.

The word "munter" spread through North Shore schools, becoming a common insult, and was soon transformed into a verb, "to munt" - initially used to imply the occurrence of unwanted anal sex but later evolving to describe any form of serious misfortune or hardship - e.g. being tackled after receiving a hospital pass, experiencing a devastating earthquake, etc.

The use of munted as an adjective evolved from there.