Short for Hard Kunt. Often used in Australia and made popular by ImMrTeddy via his Youtube video: How to be a HK (Hard Kunt).
They are menace to society.
They are most often seen at Mirrabooka, Armadale, Northbridge and all those other dodgy suburbs.
I went down to Mirrabooka today, so many HK's.
Did you see what Adam is wearing? What a HK!