This one always made me laugh when walking my old 85lb English Bulldog who growled if we walked past anyone:
"Does your dog bite?"
"Yes, please don't try to pet him, he bites anyone he doesn't know"
"Oh, wow, can I pet him?"
"Sure, if you only want to have one arm for the rest of your life"
and then they'd still proceed to try a good 75% of the time