My yorkie (Caillou) is a year and eight months. He has always been around a lot of people and around dogs (dog parks & neighbor dogs) and always been super friendly. About 6 weeks ago he started being aggressive towards other dogs and growling at people. What concerns me most is the way he lashes out at dogs. He will not bite but comes very close to it... even dogs that he used to be friendly with. I think it started after he got his boosters for rabies, distemper combo, and bordatella. He got rabies and distemper combo same day and bordatella about 5 days after and 3 days after his bordatella he started a beginners dog training class at Petsmart. That is the first time he ever lashed out at a dog. The dog was a puppy golden retriever who was not being mean. Since then the aggression has continued. He is super loving and sweet with me or people he knows.He is NOT neutered yet but is scheduled to be neutered in about a month. Does anybody know what to do or had a similar experience? Is it the shots, the class, or his unaltered state?