Damnation

Explosive crates are literally everywhere in this game and shooting them with any weapon causes them to explode and damage anybody in close enough proximity. It's fair to say that if you aim for all of the barrels during your campaign progress then you will unlock this naturally but it's more instinctive to aim for enemies so it might turn out you need to farm some of the kills. If this is the case then Boomtown is a superb spot and is literally right at the start. After you take care of the first couple of onrushing enemies, head into the tunnel and as you come through the other side there will be a few hostiles up on a platform with a stack of barrels next to them. You can even edge your way out and take a shot at the barrels whilst avoiding getting shot at but once the barrels go up and the enemies are dead, you can reload the last checkpoint and do the same thing all over again until the trophy unlocks.