Back Home Achievement in Dishonored
You grabbed a live grenade and threw it back, killing an attacker
How to unlock Back Home
Occasionally Overseers (the masked guys) will throw grenades at you, which you can pick up with and throw back with like a traditional item you can pickup and throw. You may want Time Bend for this to make it a bit easier. The achievement can be a little glitchy, so try and kill the guy by getting a direct hit with the grenade, which seems to work 100% of the time.
In mission 2 is a great place to do this. After entering Holger Square you have to help a trapped guy named "High Overseer Martin" (cannot be missed). Right in front of him is a normal Overseer. Just make some noise and run around until he throws a grenade at you.