Teddy, my pomeranian, was very aggressive when he was a baby. We was just a few months old and probably 3 lbs. The groomer was so ticked off when I picked him up. She said she had to muzzle him, he has the worse attitude, and I'd better not ever breed him. I don't know what changed, but that only lasted a month or two. He's a sweetheart now. I think someone just had to let him know that hoomans are alpha. He also used to snap at me if I took his bone.