You're preaching to the choir here. I'd venture to guess that everyone on this thread has been on the receiving end of that kind of inconsiderate behavior. I know that my patience has been tested more than once at Nod Brook by the great clueless masses who have chosen not to train and/or leash their mutts.
They have no idea why I don't want to let my dog "play" with someone's untrained cur, and they get offended when I ask them to control their dog as the mutt tries to chase and/or hump my retriever as he is returning with a training bumper, or sitting waiting for a hand signal from me. In one instance, it was a good thing that my training pistol was only loaded with blanks!