To my regret, I did not make a side trip to New Zealand when I visited Australia decades ago. (Was preoccupied with a friendship there at the time.) Thus, I'm somewhat ill-informed regarding the term "Boi racers."
Here in the Washington, DC, area, we have a surplus of small Honda autos (there are others, but Hondas seem to be the most prevalent) with huge, hollowed-out coffee-can mufflers (silencers). Some, though not all, are lowered, a la the "low rider" concept (though generally lacking the hydraulic "bouncers" of low riders. A common characteristic of their owners is that they appear to spend all their money on exhaust system, wheel rims, and (sometimes) exotic paint jobs, not safety and performance items. A mechanic friend tells me that the suspensions and brakes of many of these cages are totally shot, making them "misguided missiles" on the roads.