I have an 8-month-old American Pit Bull Terrier. He has always been so friendly with people and other dogs. Now, he is suddenly aggressive towards anyone and anything he is unfamiliar with. It seems like it happened overnight. He barks, lunges, and growls at passing dogs and children, and anyone who dare try to pet him is met with loud snarls and snaps. He is not trying to hurt anyone or bite them hard enough to cause pain, but this is a really alarming change in behavior. I have to muzzle him when we go outside, not because he is overly reactive, but because people think he is too cute to resist and will approach until their arm is right next to his face before asking me if he is friendly, or not asking at all. His parents and litter mates are not like this at all. Someone told me that the runts of the litter were more prone to aggressive behavior, but there are two other puppies his size in the litter and they are both friendly. He is the only one that is not. When we go over to visit his family, they will happily greet visitors with a few barks and a wagging tail, while he will howl, jump up, and nip at the intruder's clothing. I don't know what to do. I got him because I thought he would be a stable, friendly dog. He is an angel with my friends and family and warms up to people quickly. I would never dream of getting rid of him, but this behavior needs to stop - fast! Is there anything I can to to "fix" him, or at least make the behavior manageable enough so that I am not embarrassed to take him out in public?