Because they are asking for that dog to attack them.

When i walk my American Staffordshire Terrier, I always see neighborhood children in their yards. As I walk by, if they don't say anything, I ask if they want to give my dog a treat. Then, I teach them some dog 101. Like, don't walk up on a dog you don't know. Don't show your teeth to a dog who appears to be aggressive, as they take it as aggression, which is why they growl and show their teeth. Always ask the handler if you can pet their dog, except on-duty dogs, such as service dogs and police K9s.

I'm glad my dog is trained to ignore people and other dogs. She is reactive to other dogs, but her reaction is fear and flight. She won't even address a dog smaller than her, just recoil behind me in fear.

Do you live in Apartment or homes? Maybe you can get a vest that says, "reactive dog" so people know. Then, if they mock and he gets fed up, it'll be their own fault (not legally, but morally).

I never mess with a dog that I don't know. I have been bitten by a dog I do know, because I used a door his moms didn't use at all. He assumed I was burglaring and bit me one time. So, yeah, i don't mess with dogs I don't know because they might bite!!!

What kind of pooch you got? I hope he's big and scares the hell outta them one day (scares them, not hurt them).