Monty and Kiki will bark or growl at certain people when we walk in our neighborhood. It's more towards older men and women. I'm sure it stems from abuse they suffered prior to coming here to live. Kiki even reacts to older people on the TV. When they display this behavior on our walks I yank on their leash and say NO...BAD, Stop and they do. Yes it is embarrasing and I will never know what exactly made them do this. It's getting better with work, They are super with my young grandaughters, kids on the street, people that visit our home. All I can say is try what I do, yank and say no, bad, and teach the down and stay. That's very good for any dog to know. Good luck.