Back in the 70's, my son had a basketball goal on the driveway of our former house. There were often a group of boys from the neighborhood in residence and most were well behaved as they shot baskets and played horse. There was one who didn't always act in a good way, and his fun was achieved by sarcasm and trash-talking my boy, who was at least 6 years younger. I stood inside the house, watching and listening one day. I happened to pass in earshot and didn't like what I was hearing. When the mean, nasty, degrading talk became more than I could take, I went out and told the kid to go home if he couldn't treat my boy and my yard with respect.
He started to leave, tossed the ball over his shoulder and turned, saying..."Kiss my ass." From somewhere deep down inside, a memory of an insult I had learned 20 years earlier, I replied....."It looks too much like your face."
For several days, I berated myself for talking in a manner that was actually down on his level, and for saying in front of my boy, who was about 8-9 at the time. Finally, I sat my boy down and apologized for getting involved, and for what I had said.
Know what he told me? That the kid had a great deal of respect for me now that I had answered him in kind - and he probably would not be bothering my boy again. And he didn't.