In 1948, Vogue published its 658-page Book of Etiquette, compiled by editor Millicent Fenwick, featuring how-tos, dos and don’ts, and the proper politesse for a remarkably varied set of scenarios. But as Fenwick writes in the introduction: “Etiquette is based on tradition, and yet it can change.” Some 75 years later, Oh, Behave! is a new monthly Vogue column in which experts sound off on today’s ever-evolving social etiquette.