Fist shaking

Zach is still indifferent to the new puppy but man he is getting sassier by the minute. We were sitting on the floor and I started picking up books or cars or something. This organizing was unacceptable to Zach so he pulled my hair so I would look at him (to be fair I had no idea he was talking to me & wanted me to look at him) then pointed his finger at me and said no mama, no, no.....all while looking me in the eye & shaking a finger at me. I was too shocked to respond so he scolded me and promptly walked away very proud of himself. I felt properly scolded. I almost put myself into timeout before I realized I'm the adult here. I better get a handle on this whole being in charge thing or I'm in for a world of hurt in the future....but really, how do you respond to a toddler fist shake. Where is the section on toddlers acting like teenagers in the parenting books?