The infamous "No"

Our little boy has figured out the most important word in his very young vocabulary, and he's quite proud of it. His use of "no" - even though so cute and endearing - has really cropped up overnight. It's amazing of his understanding of time-outs and consequences for his actions, but I'm thoroughly impressed with his use of the "no" so defiantly when he thoroughly does not enjoy something you ask of him. In fact, his vocabulary seems to broaden daily. I think to myself - where'd he learn that? I wish I could say everything he learned, he's learned from me, his daddy or his sister...but he's exposed to so many other children and great adults daily. His observation of anyone seems so adult for a little toddler, like he knows how to people-watch and be friendly all at the same time. Granted, he still walks one way and looks the other, but he's starting to put all the pieces together.