While stereotyping is wrong, it's not hard to see where he's coming from. After you pass a couple of 911's that are going 5 under the speed limit, that gets stuck in your head. You forget about the 911 a couple of days ago that screamed past you on the interstate, only the slow ones you remember.
I hate ricers with a passion. I have met some people that drive them and they are straight up douchebags. However, I have met some that do it to be funny. A guy I knew had paint chipping off the car and was missing a couple of hubcaps, so to be funny he got a huge ricer spoiler for the back. Nice guy though. Messed up sense of humor, but you get the idea.
Vette drivers are definitely douchebags though.