Easy method
Start up your game with 3 controllers plugged it and go to CUSTOM GAME then select LOCAL.
Next go to the second game mode called BATTLE ARENA and from here select NEON DOCKS.
Place the 2 IDLE characters next to each other then drive around till you get the HOT ROD weapon. Use the weapon when next to both players and the achievement will pop.
There is a time limit but you will not need the whole time.