It’s tough reaching a Robert De Niro level of famous. You have to go on these talk shows like a monkey, but really, all you want to do is drink a cold — extra-cold — martini in silence. Mensch that he is, Stephen Colbert indulges De Niro with just that. It butters him up enough to allow Colbert to pitch him his script idea for Three Santas, where he plays the real Santa Claus, who has to fight off two imposter department-store Santa Clauses. How do you determine the real Santa Claus? How do you determine the real Robert De Niro?