Hi B. S.
I want to tell you that I do also have a 3 year old daughter very bossy and pretty much she want to do what she wants. This is new to me because my son was not like that he was very easy going and a good kid. I have talked to a lot of people about kids behaviors and they narrow it to a couple of things.
The first thing is you need to see what kind of nutrition you are giving your son. Lots of the foods for kids have lots of sugar that truly the human body does NOT need. for example Juice, cereal, canned fruit, even milk has glucose. In addition if your son likes candy, chocolate milk, cookies, etc that is even worse. You need to cut down on sugar and more natural fruits and vegetables, but if you do that for your son, then you need to do that for the whole family because he can not just sit and watch. Reducing the sugar intake will help with his attitude. Sugar gives him too much energy that the body does not know what to do with it and then the doctors call it ADD.
Second, is what you do with his behavior and the interactionwith your son. For example I spoil my daughter so much and she always gets her way, but this is wrong to an extreme. When your son has the episodes dont make a big deal of it, because he is doing it to get your attention and when he does he wins. So, just talk to him and let him know you dont appreciate what he does. Let him know there will be consequences for what he does and stick to it when he is mean to other people. Teach him to say sorry and eventually it will get a little better. Spend quality time with your son and give him attention when he is not having his episodes.
I am going thu the same thing with my daughter and she is getting a little better, and it is very hard to discipline her because I love her and dont want her to cry, but some times we have to be stronger and dont always give in. In the long run it will be a lot better.
I hope this helps :(