don't do it. you don't know who he was talking about or the circumstances. no need for you to get involved. if he wants to be a jerk with other people and say crap let him. is what he says impacting you? then deal with it, if not, then don't. pick your battles. don't be a pain to management over little crap.

plus they could have been talking about someone totally not work related but that they both knew. bringing it to management would make you look foolish.