I usually just like, apologize. Half the time I shoot somebody out I just yell, "sorry!" I don't know why, though, and I guess it's not the most intimidating thing in the world to say, but, there it is.
Sorry works. It's usually more confusing to an opponent if your polite to them then if you try to intimidate them. It's like when I played football as a kid, it seemed to mess up a dudes head more if you helped him up and brushed the dirt of him after knockin' his ass to the ground than insulting his mother or something. The trick was to do it every play.