In my experience this is normal. Most children will reach the age of testing you and seeing how far they can go. It's your reaction there waiting for. 2 things I tried that worked were these... I would bend down and talk calmly into my sons face and ask him to do something. If he refused, i calmly went and took a toy and threw it out...(not really, but he thought i did)... He would scream and cry, and i would calmly do it again. He VERY quickly learnt that if the behavour continued, he lost more toys. When being good, i would pull him aside ,tell him how good he is, and give a toy back. It worked a treat!!
It didn't work with my daughter, so i went the other way. After some really disgusting behavoir, i emptied her room (DR Phil style!). When good, she got back something I'd taken. Worked on her!! I dont have perfect kids, but there pretty great. They've learnt they have to be respactful, and that good behavoir is rewarded. Hope I've helped, and good luck!!