My Wrongs 8245–8249 & 117 (2002)
My Wrongs #8245–8249 & 117 is the first film by Chris Morris, starring Paddy Considine as a mentally disturbed man taking care of a friend's Doberman Pinscher (named Rothko, and voiced by Morris) while she's away. The dog talks to him and convinces the nameless protagonist that he is on trial for everything he's done wrong in his life, and the dog is his lawyer. Unfortunately, the dog tends to make things worse for him, and the man's life falls further into disrepair.
More at Wikipedia.