FlatOut 4: Total Insanity

If you haven't achieved this through natural career progression (like me), then this is how I went about it.

Game Type: Quick Play
Mode: Race
Type: Racetrack
Track: Redhook Invitational Collision Course
Ambiance: N/A
Nitro Gain: 200%
Damage Modifier: 200%
Race Length: 10 Laps

Vehicle: All Star Class, Rocket Sorbet Van

Method
This is a short, compact circuit, ideal for smashing other vehicles. You can easily go backwards around it, which is critical for ramming on coming traffic. Do one normal lap, then start going the opposite way at the figure of eight and Nitro boost into traffic as they are coming around the track. The Sorbet Van is very strong and should easily destroy 3 smaller cars before wrecking your own. Try to aim for the weaker cars, but any 3 vehicles will do. 10 laps should give ample time to wreck 3 opponents :)