After you've completed the Supermarket mission, two side missions for Rocco will show up. Go start the leftmost one (right in the south section of the map), entitled Bet on That.
For the first part of the mission you follow the guy on foot, then in a car. When you get to the place where he stops, kill all the enemies then grab his car, a Delizia Grandeamerica. Go to the safe zone to finish the mission.
Now for the actual achievement. First and foremost, upgrade the car to level 3. Next you'll have to start a mission so you can actually gain points - I would suggest one close to the highway, like Wheels of Evidence. As a bonus, if you die/screw up the car, you'll go back to the checkpoint right before starting the mission so you can quickly try again.
Once this is done, head to the start of the highway close to the big bridge and start driving down the long straight road along the river. Now it's a simple matter of gunning it, go as fast as you can and stay in the middle of the road (you can honk the horn to get cars out of your way). You may have to go around the first turn but just slow down a little bit and you should be fine.
You should get 2000 points during this corner, after that slow down to stop and when the points register you'll get the achievement.