"Some dogs love all other dogs.
Some dogs are good with other dogs they know well -- but not with strange dogs.
Some dogs are good ONLY with other dogs of the opposite sex.
Some dogs are tolerant with puppies -- but not with other adult dogs.
Some dogs are fussy about the SIZE of the other dog. They may dislike large dogs. Or they may dislike small dogs.
Some dogs are fussy about the BREED of the other dog. They may be fine with their own breed, but dislike other breeds. Or they may be fine with other breeds, but not with their own!
Some dogs are aggressive or timid with virtually every other dog."
No Dogpark for our future!!
Haitis recently developed an aggressiveness to all other dogs that aren't in his own pack. He is only 7 months old now but today we returned for a refresher intermediate class at our Petsmart training center. He was lunging and growling/snapping at any dog within close range.

No matter breed, color, or sex. At one point he was lunging and growling but still had his tail wagging. :? Other times he had very dominate posture.
My trainer tried encouraging me to keep him in our present class and also enroll him in Doggie Daycare. She wonders if he might act differently at a Daycare when I wasn't around him but I don't have much faith in that.
I wish I
could socialize this characteristic out of him but I won't risk having him attack any other dog, and I don't like the way (some) people looked at him today when he briefly became assertive in their presence. I tried to tell them he was just a pup, more like a teenage boy but I could still feel their stares.
I know I did well making sure all encounters he had with other dogs were as postive as possible, as a young pup. This recent negative disposition and posture in the presence of any strange dog must just come from instinct because he has been neutered since he was 4 months old so I've ruled out sexual maturity.
I can live with this, I guess and be a responsible owner, but it truly breaks my heart because I wanted him to be a socialble boy. I'll probably discontiue his Petsmart training and seek private lessons which can still be rewarding for both of us.