Hugh Hefner's Christmas was extra, extra jolly this year: He's engaged again! The Playboy founder, 84, is engaged to Crystal Harris, his 24-year-old girlfriend and Playmate, a Playboy rep confirms to UsMagazine.com. Hefner first Tweeted about it on Sunday. "When I gave Crystal the ring, she burst into tears," the Girls Next Door star wrote. "This is the happiest Christmas weekend in memory...I got what I was hoping for for Christmas...Crystal's love." To make his news absolutely clear, the mogul then added: "Yes, the ring I gave Crystal is an engagement ring. I didn't mean to make a mystery out...