Explosive Surprise Achievement
Kill 5 enemies with sabotaged vehicles (Campaign only).
You’ll first need to unlock the "Saboteur" perk before you can sabotage any vehicle. Feel free to follow this up with buying the "Booby Trap" perk to help.
To prepare for this achievement, travel to any hostile territory and wait around on the road for an enemy vehicle. When the vehicle approaches you, shoot the driver and then wait for the vehicle to come to a full stop. Now quickly make your way to the hood and press to tinker with the engine. The enemy riding passenger should, during this time, jump out of the vehicle and take cover on his side of the truck (and stay there if you crouch and hide). After about ten seconds, the vehicle will blow up and likely kill the enemy so long as they were close.
After this happens, proceed to any other fast travel location in an enemy-controlled territory and repeat the process over. The achievement will unlock once you have killed five enemies in this manner.