What is up with the sport bike/Harley animosity?

I notice that bikers usually give each other a wave when meeting on the road. I also seem to notice sport bikes don't tend to get (or give) waves to Harleys, or similar bikes. I asked my friend why that is (he has a Ninja) and he said he didn't know, the two camps just don't wave. So anyone have any ideas as to why this is?