Classic grumpy, bitter old people. I am sorry they are taking their anger out on you.
I will tell you a story I think is great along this line: A friend of mine is disabled because of fibromylagia. Obviously that doesn't show. So, one time when she parked in the disabled spot with the appropriate card showing in her car, a lady came up and fussed her out. When my friend finally got a chance to get a word in edgewise, she explained to this lady what her handicaps were and why she was disabled.
After the lady listened, she snapped, "Well, you ought to have a sign around your neck explaining that that's what wrong with you!"
My friend's teenage daughter who was overhearing the encounter had had enough, so she spoke up and said, "Well, lady, in that case, you ought to have a sign around your neck that says, '*****'!" (rhymes with witch)