Throughout “Maphead,” Mr. Jennings comes off as a student desperate to prove that he is the smartest kid in the class. “The first time I saw Mikhail Gorbachev on TV, I remember thinking immediately that his famous birthmark looked just like a map of Thailand.” Maybe he did. But back in the day, “Saturday Night Live” made the same joke, about the Philippines. When Mr. Jennings knocks John McCain for saying, during a radio interview, that Spain is a part of “Latin America,” he can’t stop there, in recognition of the fact that politicians utter innocent misstatements all the time. Instead, he piles on in, of all places, the book’s index. The entry for Sen. McCain reads, in full: “McCain, John, senility of.” A later crack about the stench of “homeless Internet users” at public libraries is another graceless putdown.