It happens sometimes that a dog, who is known to get along very well with other dogs, meets a dog he obviously has problems with. On the other hand, every once in a while a shy dog meets another dog and seems to "flourish" in his company and becomes active. Notorious troublemakers appear to be changed dogs if they meet the "right" dog.
People are often confused, because a dog's affection or dislike towards another dog is not related to breed, size, age or sex.
Take a look at your dog from a different perspective. Take into account his history, personal social needs and tasks. You will realize that certain behaviors are firmly embedded within him.
It is important to learn, know and appreciate a dog's different forms of communication. This will help you to understand your dog and him to understand you.