Yeah, really, I'd say that it's more that Chris is muttering at people than to himself. Chris wants to bitch at people, like if they complain about his beloved mcdonalds, but he's too much of a pussy to stand up and say it to their face. So he just mutters with his face in his food at them. He says shit like "if it's not good enough, just cook it yourself!" over and over. They can still hear it.
Heh, although other people aren't allowed (in chris' opinion) to complain about their messed up orders, he'll turn around and then bitch if his order gets messed up. Like if his sandwich has pickles on it.