Tasked with the peculiar and peculiarly thankless job of explaining Cam'ron to your mom, Times pop nerd Kelefa Sanneh does more than keep up with the Frere-Joneses. He also has steadily built up a jaw-dropping catalog of double and single entendres based on the recordings, videos, and live performances of the surrealist and probable pederast Robert Sylvester Kelly, as Friday's review of a show in Columbus, Georgia (you know, the seventh borough) reminded us.