Well, for starters the accent they have when speaking english is awesome!! South Park has done a great job highlighting that!! They also have a peculiar driving style, almost oblivious to other drivers and posted signs!
South parks way of showing Asians seems racist to me. It's only funny because of the stupid things they do. It's just so stupid that it's funny. So if you relate Asian people in reality to Asian people in south park then you are seeing asians in a wrong way.