Cosmic Smash - 10G
Very easy to obtain this achievement...
Select ''Custom Game'' at the main menu and connect a second controller and select ''Local''... Choose "Battle Arena" and "Neon Docks". Now with those settings enabled you will have no enemies to take the bonus boxes and more of a chance of getting the "Hot Rod".
As long as you hit A when the hot rod is shaking and smoking and just about to go into the red on it meter like Zarakai1989 said above, the achievement should pop and only take you a few minutes to get :-)
Alternatively just keep trying while playing through career.