Let's imagine you meet an old friend.
You are sincerely happy to meet her/him, but suddenly your friend says something tactless and unpleasant. It would definitely hurt you and you'd like to retaliate.
Should you actually do it?
Well, if you want to respond to a stupid provocation, everything is in your hands.
Or you can pretend that you didn't notice anything, that means that it's absolutely doesn't matter to you. In this case, just say nothing.
By the way, if your opponent expected your reaction to her/his aggression, the lack of response will embarrass her/him for sure.