Billy Bob Thornton’s extreme dietary restrictions have inspired him to get creative with his snacking, which is how he found his new favorite unlikely pairing : grapes dipped in dijon mustard. The 70-year-old actor opened up about his health problems during a recent appearance on the Howie Mandel Does Stuff podcast. “My diet's very restricted,” he said on the May 5 episode. “Well, I'm allergic to wheat, dairy. I have type AB negative blood, which is the rarest type in the world. It's like less than one percent of the population of the world has it.” The Bad Santa star said that his blood type means that he has a harder time digesting certain foods.…