I'm in a fighting mood, how do I calm myself down?

Let's just say that someone said some things to me that they had/have absolutely NO RIGHT (do not ask) to say (and for no particular reason.) Being provoked, I replied saying that they should not even think about telling me about this particular topic again. After I left the room, I [definitely] heard them say [to me] "shut up." However, I believe that they meant for me not to hear it. Regardless, that further provoked my fighting mood, but I decided to leave it at that...for now. I know I am better than this and I honestly hope to handle this situation maturely (even though the person who I am quarreling with is two years older than me yet exceedingly immature) rather than with harsh profanity, which I am incredibly skilled at. As of now I have isolated myself from my "opponent". I do not wish to provoke any hostility the next time I see him, which can be in any second, yet despite this fact I do not take too kindly to ANYONE who talks to me in such a manner as the way he did. How do calm myself down so that I can handle this quarrel in a mature, no profanity manner?