As many of you know I have a CC pup Rocky who is now 6 months old and about 75 lbs. He has been dog and people socialized , been to puppy agility and to many settings where dogs and people are present. My son assists at a dog training facility so Rocky goes quite often and is a "star pupil" My son was asked to come to class to assist with a 1 year old EM who weighs 133lbs..no dog socializing and just because of his nature hes good with most people.. Rocky also went and my son said from the minute he entered building Rocky wanted to meet the EM.. ( 1st time a dog was double his size..he's met dogs up to lbs ) when they met EM was pulling his owner so hard they had to assist her...rocky was doing "puppy bow" wagging and all happy..as soon as my son went to help with EM..Bam he got all full of himself..lunging at EM ..hair on end..and not listening worth a crap..(I came in at that moment and grabbed his lead and took outside) even with me he was intent on this EM and his Body language told me that he did not care how big he was.. all googly eyed up puffing out his jowls , full wrinkled brow etc..I had trainer grab EM lead and even with my son holding him Rocky wanted this dog. At 1st I thought Rocky was just pi$$ed my son was holding EM..but he holds a lot of dogs during classes and Rock does not act out like this. Now I am thinking it may have been the dogs size and Rocky was trying to dominate..to be 100% honest this behavior caught me so off guard I did not respond as I would have at home. He was only on a harness and was pulling for all he was worth.. Just looking for ideas..I know its hard not observing yourself but any thoughts will be welcomed. BTW the EM was barking at him and lunging also..