We rarely see Robert DeNiro’s vulnerable, personal side. But yesterday on Katie Couric’s talk show, DeNiro spontaneously burst into tears during an interview alongside “Silver Linings Playbook” director David O. Russell and co-star Bradley Cooper. Russell had been talking about his own teenage son who suffers from mood disorders. When Katie asked DeNiro if he identified with Russell’s description of what he goes through as a parent, DeNiro started crying. It comes at about 5:10 in the video below. Back in September, when “Silver Linings” debuted in Toronto, DeNiro — I wrote this then– came out of the screening with tears in his eyes. DeNiro is just the nicest guy, and he does not ever sell his life’s problems to get attention. It’s the last thing on his mind. But “Silver Linings” is about fathers and sons, a father who is highly sensitive to his adult son’s emotional issues. DeNiro had that with his father and has it with his own teenage son. It’s one reason, I think, he held off doing much press on “SLP” until now. Again, a rare moment with a really good fella.