"I didn't mean to be hurtful. Why would someone be hurt by that? I was just trying to be funny. Some people are too sensitive. Besides, it's true. ..." And so on, and so on.
From the article:
"But I don’t always have the time and energy to do that. And sometimes, even if I did have the time, the person involved doesn’t want to be educated. This is when I pull out “we don’t do that here.” It is a conversation ender. If you are the newcomer and someone who has been around a long time says “we don’t do that here”, it is hard to argue. This sentence doesn’t push my morality on anyone. If they want to do whatever it is elsewhere, I’m not telling them not to. I’m just cluing them into the local culture and values. If I deliver this sentence well it carries no more emotional weight than saying, “in Japan, people drive on the left.” “We don’t do that here” should be a statement of fact and nothing more. It clearly and concisely sets a boundary, and also makes it easy to disengage with any possible rebuttals."