He quickly became obsessed with a Little Tikes Cozy Coupe; a toddler sized plastic car that had a door he could open and close himself. He would open the door, get into the car, and then close the door and move the steering wheel around for a few seconds. Then he would re-open the door, exit the car and repeat the process several times. He loved it.

My son did not stand for this boy usurping ownership of the car. He promptly crawled up to the 18 month old, grabbed his hair and pulled it as hard as he could. I was horrified. I ran up to my child and exclaimed:
"Hey! What are you doing?! No! Stop that!" I removed him from the scene of the crime and comforted the other boy who, at this point, was screaming his tiny head off.
I felt terrible. Where did my son learn such rude behavior from? Certainly not from me. I had never seen him do something so blatantly mean to another child.
The other boy calmed down and the kids went on playing as usual. I was relieved. Until a three year old girl (the sister of the boy who my son just got finished torturing) approached the Cozy Coupe. The girl got into the car and began driving. My son was visibly displeased. He opened the door to the coupe, and pushed the little girl to the side using the force of his 22 lb body.
What was happening? My son was so fixated on this car that he was unwilling to let any other children use it, and it wasn't even his toy to begin with!
I could not believe my son's behavior. As much as I tried to intervene, he was behaving like a bully toward these children and I felt powerless to stop him.
I began to wonder if this is his true personality coming out. Images flashed through my mind of my boy five years from now on the playground, smacking a child in the face and running away and feeling no remorse in the process.
Is this who my son will become? I am going to observe him closely to see if this behavior resurfaces in other envrionments. If it does, I must find a way to stop it!