Before starting be sure to play many games offline and online to unlock items for your car; you must have the mohawk unlocked before this achievement can be earned.
Once unlocked, equip the mohawk
After equipping the mohawk, go to the main menu and select exhibition
from the options. The map must be set to Wasteland
, as it says in the description.
Edit the mutator settings
and change the preset to Demolition
as these will already have the presets necessary to make it easier. Make sure to put a minimum of 1 opposing bots
however it will be quicker and easier with 4.
Once these are set, start the game and simply crash into the opposition. Be careful and check that your collisions are counting as your demolitions as it may count against you.
Rinse and repeat until the achievement pops.
For a demonstration and explanation, check out this video for more information.