A: ADULTERY
As ubiquitous as alcohol and tobacco in the Mad Men universe. Leading the pack of strayers is Don, who stepped out on his wife, Betty (January Jones), with at least four mistresses, including Bobbie Barrett (Melinda McGraw, above). Unapologetic rogue Roger Sterling left his wife for Don's secretary, while Pete Campbell, Harry Crane (Rich Sommer), and even lily-white Betty have all had extramarital flings of their own.