Earlier this year, I was at a Hyde Park in northbridge with some chinese friends of mine during chinese new years'. Big event, heaps of families there sitting on the grass. Midway through the lion dance, A couple of viets sprint through the middle of the park, and hack another vietnamese guy to death with machetes- in front of several hundred onlookers. You try not be racist (hell, if I was that much of a Pauline Hansonite, I wouldn't have been hanging around with chinese friends, now, would I?) but things like that do color your feelings. As usual, its just a case of a few bad apples creating a negative stereotype for the rest.
There are some clubs in Northbridge where I would never go on certain nights, simply because they're frequented by crazy vietnamese gangsters, who pick a fight with anyone who looks at them, carry knives, and fight dirty. I'm guessing the situation in Melb is similar if not worse.