pop-up boonga 

A Polynesian/Pacific Islander who hides behind a fence in South Auckland, and then "pops up" without warning to throw a large rock onto the road. These creatures often work in packs and one should drive quickly through such areas to minimise a "pop-up" attack.

"Mate, I'm heading down to Otara today to pick up some weed."
"Oh, be careful for Pop-up boongas mate, they might throw rocks at you"

pop-up boonga by HOB November 1, 2006