You have to have dimsum, wonton noodles, the street food and clothes shopping in Mong Kok. There's a street that sells a lot of unique things along with knock-offs, i don't remember the name right now, if you plan to buy things there, make sure you haggle, pay at least 1/2 of what they want.
For the bar scene, go to Lan Kwai Fong.
Enjoy!
Welcome to my hometown. Enjoy your stay. I hope your hosts will show you an authentic side of HK. PS. You won't find used panties vending machines in HK. That's supposedly in Japan. ;) -Ivan (Acuraworld)