I was staying at a really crappy motel-type place in Wan Chai many years ago, woke up to a bunch of yelling. Looked out the window from the 3rd floor and there were about 30-40 guys going at it for quite a while, then they started to splinter off into the alleys. Almost exactly like 古惑仔 style
Another time was at a rave, walked outside and there was a big gathering of over a hundred guys facing each other, they formed 2 groups with a gap of about 10-feet between them ... my retarded friend decided to walk BETWEEN them and I had to drag his ass back and we took off before they started to "pek yau".