1. Hit right on the dpad to open Easy Drive.
2. Select multiplayer.
3. Select Create Friends Game.
4. Invite a friend to your game.
5. When they join, meet up and ram them to take them down.
Best done when your friend is stationary. Having them switch to a light car like the Ariel Atom will help as well.
If you need a friend, try looking at the Boost List
and asking nicely.