Surely if both dogs are on a lead, like they should be, then this wouldn't happen as both owners are in control of their dog? I'm sorry there's just no excuse for walking your dog off the lead in a public place, no matter how well trained you think it is. I appreciate that you think yours is well trained and wouldn't hurt a fly, but you just never know, even well-trained dogs can turn and bite.
I couldn't care less, I'm not interested in playing, people just need to get their dogs on a leash and keep them under control!