Let me list the fun things you can do in Sleeping Dogs:
1. Do a wheelie and ride on the wrong side. When a car approaches, it works
like a ramp and you jump real high, and then you can keep jumping over cars. 2. Leave the bike when in air and watch it destroy other people/vehicles.
3. When in air on the bike, try to do a wheelie and fall on the back, preferably on other people.
4. While driving, use your car door as weapon to bash people and other bike riders, like this: http://www.youtube.com/watch?v=JAXSbpC8qI4
5. Grapple random people and throw them in water, and watch them die as apparently only Wei can swim in game.
6. Use things like umbrella, purse, fish, etc to bash people. There is an achievement for beating up people with fish XD
7. Take a bike to your apartment and park it there.
So what else can be done?