Normally, I just try to match them--smile for smile--but the incongruity of the situation bugged me.
I asked him if he knew what today was.
Naturally, he didn't--no reason why he should.
I explained to him about Tisha B'Av, about what happened on that day throughout history: including the Crusades and the Jews slaughtered by the Crusaders on the way to recapture Jerusalem.
His response: Well, that's your opinion.
I told him, no...it's historical fact.
His response: That's your opinion.
Rather than lose my temper, I went inside...where I thought about all the come-backs I could have said. For instance, I could have responded that some of his beliefs were based on opinion.
My favorite response would have been the 'Muslim' response, something filled with outrage like this:
What? Jews were killed during the Crusades and you say that is merely an opinion? Six million Jews were slaughtered by the Nazis--and you're telling me that is only an opinion too?! How dare you desecrate the memories of Jews who have been murdered...Of course I would have been twisting his words, making a scene, and possibly intimidating him and the rest of his group, but it does seem to work.