For this you need to have a green icon next to your name, which means you haven't been hitting anyone or anything in a few races. You can boost this by setting a jam session up with a friend and just drive carefully to the finish.
You can also do it 'legit' by going to Pro Tour -> Skirmish. When the race starts just sit there for a few seconds and let your opponents drive away. Then just drive slowly towards the finish, staying last and not hitting anything or anyone. You will probably not finish the race but that doesn't matter.
I got this after 4 races and I've had a red icon a bunch of other times before so that shouldn't matter.