Another achievement with a Zombieland reference.
This one is very simple to do and can be done shortly after you get to drive your first car.
This way there's no need to get a zombie to cling to your car door.
While driving (RT) hold down X (you'll hold the door open), line your door up with a distant zombie and drive the door into it with decent speed.
I got this on my second attempt, the first time the Zombie bounced off the hood and didn't die. The second time (a different zombie) it died instantly on contact with the door so you may need to kill it in one hit.