Why would you type shut up? What are you going to accomplish by that?
What the fuck do you think their first impression of you was when the first and only thing they saw you type in chat, it to "shut up"?
Let's take a guess:
You have 3 other people on you're team who don't deserve to listen to YOU flaming, and THEY don't give a flying fuck that "ur only doing it to get some revenge", when frankly, the fool who started it is retroactively justified in his actions, because now s/he knows that you're a flaming piece of shit.
OK then.
[zombie-brand-facepalm]
But still, the fool that started it is only aware of your reaction, and interprets it as the kind of person you are. That is the point. So the fact that I can facepalm, an obvious response that many flamers have to being flamed, doesn't conflict with the idea, that not flaming back at all, is in fact the best solution to a short term problem, that will be over at the end of a game.
Try to see the bigger picture here, and you will not feel the need to flame back.