[asher]

How does a wise and tactful man react to a tactless remark in a large group?

He doesn't. He might try to direct the conversation to more agreeable matters. He certainly doesn't draw attention to the offense and impress it indelibly in the minds of the others.

Generally, you are better off improving your own behavior than that of others. As Dale Carnegie pointed out, it's not only more profitable; it's less dangerous.