2 going on 15

Little Mr. Nicholas has picked himself up a little 'tude lately and it has got to go! He has been talking back at every turn and so far my efforts to stop him have done little to curb the behavior. If I tell him to do something he blatantly tells me no followed by something to the effect of I can do whatever I want to. I threatened to lock him in his room for misbehaving and he said "I'll lock you in". Last night I put him to bed and he climbed out of his room over his gate and went into Collin's room where he proceeded to open all of the drawers on one side of his dresser, remove the clothes from the top drawer, climb onto the dresser to turn the light on and then turn over a hamper full of summer clothes that need to be packed away and put in the attic. Then he came downstairs and said "busted". I told him he was busted and he said "No, you're busted". I hauled his little butt back upstairs and threatened to lock him in his room if he got out of bed again. Today he gave me a smart answer to something and I swatted his but for it. He turned around and spanked me back! I put him against the wall and told him to stand there for a time out but I practically had to smoosh him against the wall with my back to get him to stay. The worst part is we were leaving daycare so his sitter got to see the whole thing. I'm about at my wits end with this behavior. Time outs don't phase him much and there isn't a whole lot that I can take away that he will miss. If I don't squash this behavior now I'm really going to have problems when he's a teenager. How can my little boy be so kind and well behaved one minute and then such a mega brat the next? Super Nanny, please pay my son and I a visit. We could really use some help.