Defiant 11 year old- not sure I can take it anymore!

Wow, that does sound awful to live with day after day, when you're feeling tired. We sometimes have the same thing in our house but to a lesser degree. I agree with the positive discipline.... if you happen to see him doing something good or right, give him lots of praise, no matter how trivial. Some kids get so used to the negative attention, that it just becomes habit for them. Try to turn what he says around; whatever you can do to turn his negative into a positive, and maybe he will start taking steps in the right direction. Maybe he's already worried about the attention that the new baby will get. BTW there's a good book for kids who worry too much called What to do when you Worry too much, a children's guide to overcoming anxiety. Hope it all works out.