You must not allow them to fool you into thinking that these aren't the rules they're playing by. David Sirlin's "Playing to Win" is a good treatise on how to be good, and perhaps the most important lesson is to play the game by the rules as written, and not by some other set of rules that exists only in your head.
(Though in this case the victim was senior enough that I suspect he was playing the game to the best of his ability, trying to humanize himself to gain the upper hand in some other manipulation game and misplayed, kicking things into the legal arena, as one does)