The bugs you encounter after being dropped into the ruins are called Creepers. They aren't too much of a threat but in groups they might become a nuisance if anything. Instead of shooting or hammering them, walk up to the bugs and come to a complete stop. Before the creepers jump away, press
and you will perform a "finisher". In simpler terms, you're going to curb-stomp the bugs.
If you kill them by swinging your arm, you will not gain progress to this trophy. You must kill them with your boots.