He's The Hound, but, if memory serves, Joffrey refers to him as "my dog" and calls him "dog."
That's because Joffrey secretly wanted to be a rapper.
Just because Joffrey does it doesn't mean we all should. If Joffrey jumped off a cliff would you jump off a cliff? I didn't think so.
I'm thinking of so many "just because Joffrey" jokes right now, but I don't want to spoil the books for those who haven't read very far.
I won't be buying Joffrey's rap album, but I will illegally download it, so I can enjoy the music without putting more gold in the Lannister's coffers.