How did you get on his good side? he doesn't like me at all 
His bark is worse than his bite. I think he was beaten in his early years and now he's scared of all humans, especially the ones in uniforms. Deep down inside, though, he's kind. Sort of like Darth Vader.
Just put everything he says into that perspective and it will go easier. Treat him with kindness and firmness, like I do. It confuses him. When he says "Fuck your mother" you'll know that you've touched him deep inside.