Basically a gun that does crap damage, but if the bullet hits a vehicle the user takes control of said vehicle, rendering it inoperable by the intended driver. Optionally, whenever a vehicle roadkills in that state, the kill is attributed to the controller and not the driver.
When the controller has had enough, he can either unequip the gun (switching back to himself and making the vehicle driver-operable again), or press the L key (switching back to himself and killing the vehicle).
It's basically this:
