Robert De Niro wasn't acting when he broke down in sobs on Katie Couric's day time talk show Monday. The usually tough-guy actor was a guest on Katie to discuss the hit film Silver Linings Playbook with director David O. Russell and co-star Bradley Cooper. When asked about the film's premise - that of a bipolar character trying in vain to fit in - The Goodfellas actor began to cry. 'Did you feel a greater responsibility about doing a film that David had so much personally invested in?' the anchor asked, following up on a question asked of Russell. 'Of...