Wow... I'm from hong kong, and i go to hong kong at least twice a year, but i have never seen people in the streets with bb guns, and i have never spotted BBs in public (like on the ground and stuff). Even in Mongkok (where most bb gun shops are) i have never seen a kid, or even an adult walk around with a BB gun before.
Edit: just to clear things up, i have never seen a person in hong kong with a BB gun in their hands. All i see is that they carry it in boxes, so they can get from point A to point B. Us Asians aren't THAT crazy... :-D