Yesterday's New York Times ran a rather long piece called "How Do You Prove You're a Jew?", and while it may seem an unconventional topic for a manners column, I'd like to expound a bit upon it. Have no fear: even if you don't have the time or the inclination to read the original Gershom Gorenberg essay, I'm only using it as a jumping-off point for this column, and I promise not to allude......