As much as this is annoying behavior, I wouldn't take it personally. Certainly you should not suspend the common courtesy rules of your family just because he doesn't want to "take orders" from you. I would find ways to compliment him more frequently (even though you may be hard pressed to find behavior that warrants praise) and offer to do something he likes to do , one-on -one so he can feel special. On occasion, after one of his argumentative comebacks, ask him in a calm manner, " Is there something bothering you that's making you so angry because you are a kind boy and saying things like you just did is not like you. Take every chance you can get to positively frame who he is,e.g. "You've got a great sense of humor., You're a really good friend to Bobby." Your consistency, in terms of your maintaining a positive, non-judgmental attitude towards him will be his anchor now and as he goes through adolescence.
Child Always Argues
Toddler and Teenager Expert Advice from Carleton Kendrick, Ed.M., LCSW