One place to easily unlock this is in the second mission. Head to the canal area (past the mime) and down to the end where there is a guy fishing. Ignore him. Head across the bridge/dam wall next to him to a small area with a crane. There is a huge dropoff next to where you are. Save your game. Set your Hook Mine to lethal and throw it onto the hook on the end of the crane. Now you want to aggro someone and get them to chase you over to here. The fisherman might work, but I had better luck with a guard. Once the guard is chasing you, run back to this plaza and stand past the crane. The guard will run toward you, the hook mine will grab them and should shoot them way into the air over the dropoff to unlock the achievement.
Some people have suggested that you can simply throw a hook mine onto the stone pylon near the fisherman and have it grab and launch him to unlock the achievement (I've seen video of it working), but whenever I tried it I found that his body invariable ran into the pillar or broke into pieces without flying off (one time half of his body went flying into the void, but apparently the wrong half since the achievement didn't unlock). The crane hook placement worked perfectly the first time.