I guess it depends on how you define elderly. :) There was an OLD woman in the parking lot of Walgreen's when I was trying to back out of my parking spot. I tooted the horn lightly, nothing happened. I tooted it a little louder, she just stood there. Finally, I blasted the horn and she finally picked up her head. I rolled down my window an suggested that she try texting in a less dangerous place.
It would likely depend on how they reacted to it. If they apologized and I was not hurt, then I would probably just say no problem. If they acted as if it was my fault then I would have a few words for them.
I was walking through a parking lot when some dingbat drove past at what I thought was a ridiculous speed. So I slapped the door and laid down behind the car. He slid the tires.