Ugh.. sorry you have to deal with nasty people. I use a prong too, even walking into a dog park. I make him sit and take it off, I have gotten comments too.. but then they shut up when they see how well he listens to me.. I digress, lol.
Point is, I now agree with people who are ignorant and clueless, unless I truly feel they want to learn or will take well to an explaination. Others "Yepp, I'm an abusive nasty owner, what are you gonna do?"
Let it roll off, you are going to encounter them a lot.