Australian slang - Out-of-control behaviour; meaning overly fun or disruptive or partying behaviour or outlandish, rebelling behaviour; revelling.
Similar to the term, 'mucking around', which can have various meanings; 1. playing up, 2. doing whatever comes to mind usually in a lazy way or without much thought, direction or real goal. 3. Fiddling and playing around to the point of not getting anything beneficial done.
He was totally running a muck at the party and he fell through the table and smashed all the drinks while dancing.
The children were running a muck all day; they drove me nuts.
He was mucking around so much that I decided to leave, as he was never going to get anything done.