You traded paint with every competitor during one offline race and still won the race.
It is recommended that you do this achievement on the first race after the introduction, as there will only be 5 AI opponents. Keep in mind, that you can do this on any difficulty, although Normal should be fine. Once the race starts, you'll want to allow the last place computer AI to catch up to you and then you should start the race.
During the race, you'll want to pull up near cars and gently rub against them using the side of your car when you can. This will allow you to keep control. Once you touch an opponent, start going for the next one. After you touch all 5 opponents, get into first place and win the race to unlock the achievement.