Herb Greenberg at CNBC has yet another edition of his “Worst CEO List.” For 2012, he had a tough time choosing a “winner,” but after much deliberation and flip-flopping Greenberg landed on Groupon CEO Andrew Mason. The company’s mistake was keeping the software developer-turned-CEO on board after it went public. Mason’s ineptitude as Groupon’s chief was evident early on, when he sent a letter to potential shareholders saying “we don’t measure ourselves in conventional ways.” The company has struggled mightily since its IPO, and Mason’s silly antics “almost make a mockery of corporate leadership