B.R.
WOW, L.! It sounds like this boy has been through some painful times. (Maybe he didn't realize they were painful, but they certainly weren't good growing up experiences from what you have had to say.)
In some ways, what you see is normal kid behavior. In this case it seems he takes it to an extreme... likely because he had no good discipline prior to coming to you. I don't think you're going to find any easy answers to this, but he needs the boundaries, and even though he might act like he doesn't like them... and really believe he doesn't... he will be grateful for them later. Try to stay calm and loving as you continue to remind him (over and over and over again!) of the rules of your household. And try to get him to understand that it's important to you that he follow those rules because it's best for him. At twelve, he isn't going to believe that easily, but he needs to hear it from you anyway... again in as loving a way as you can convey it.
You mention that both his natural parents are drinkers. Does this mean your husband isn't on board with you or is not able to fully participate in his discipline? If so, the boy may try to throw it in your face that you're not his real parent. If so, try not to let that get to you too much. Just let him know you love him, and even though he isn't your biological child, you want to be the best parent for him that you can. And, I'm sure you know this, but it would be a mistake to yield to the temtation of putting down his real parents. If he brings up anything about his real mom not being there for him, you might want to say something like "I know, and that was a hard thing for you, but I'm sure she loved you and just didn't know how to do the things she needed to do for you." I'm sure - in your position - my natural instincts would be to want to let him know how terrible I thought she was, but that wouldn't be helpful to him at all.
I wish I had some easier answers to suggest, and hopefully someone else will come up with some better ones than I have, but know that I care about what you're going through in this and will pray that you find a way to help your stepson gain more good life skills.