In order to pick up vehicles, you must have already unlocked the Kinetic Pulse ability, which is automatically unlocked as part of the early on story mission, "Forward Momentum". To perform it, hold to pick up an object or in this case a vehicle, then fire it with or .
Simply defeat 25 enemies by hurling cars at them to unlock the trophy. Note that in order for it to count as a kill by a car, the “Special Delivery” stunt must appear on screen. For added fun, rather than pick up cars that are already parked on the streets, pick up the cars that have a person inside. Not only will you kill the enemy you're going up against, but you'll be able to blow up the car and the driver inside and not gain a single point of negative karma! Two birds with one stone!