Rabbi Steven Stark Lowenstein, of the Am Shalom synagogue in Glencoe, looked out on the more than 300 people sitting in front of him and Brett Gelman on Tuesday night. “Raise your hand if you were at Brett’s bar mitzvah,” the rabbi said. About 20 people did. “Ah,” said Gelman, wearing faux-leather pants and a long white sweater and a single earring. “Now that was the one thing that kept me from killing myself! That was my only good day in junior high, my bar mitzvah. I was deluded enough to believe I had friends.” Gelman’s book tour was not...