I’ve seen it happen, once, when I was a young man, and I learned an invaluable lesson. An older guest at a formal dinner said something blatantly anti-Semitic. I was shocked and laughed nervously. Another friend stared at his plate silently. Another excused himself and fled to the bathroom. And then there was the professor, an accomplished and erudite man, who paused for a moment, then slammed his fist on the table and said, “I will never listen to that kind of language, so either you will leave, or I will leave.” The offender looked around the table, found no allies and left the gathering.