Is it really so bad to refer to an entire nation of people as frogs? Last summer, when I was giving a speech on Franco-American relations — shortly before the publication of Our Oldest Enemy: A History of America's Disastrous Relationship with France — I made a frog joke. It involved a stuffed pig, a barbeque, and, well, you sort of had to be there. But it was definitely a quip about the French. The audience snickered, though a few people exchanged nervous glances. They clearly wondered if it was appropriate to laugh when somebody referred to the French as...