MISSABLEWhile this trophy is technically missable, you will most likely get it automatically during the normal course of the game. Also, although you can do it with virtually any weapon (like an assault rifle), your best bet is the shotgun because the bullets spread and can damage more than one enemy.
If you don't get it during your first runs, you'll definitely get it when you use the Rocket Launcher, however, if you want to get this trophy out of the way before, here's a video with an early place in the game that is quite suitable for the occasion.