I used to live next to an eye hospital. One day, walking home, I was stopped by an old man who clearly had trouble seeing. He asked me to help him across the road to the hospital. I agreed, and he grabbed hold of my hand very tightly. At this point I noticed his fingers were stained brown from tobacco, covered in scabs, and his fingernails were very long and dirty. I started to think that my good deed for the day would be a bit regrettable.
When we got to the other side of the road he still had my hand grasped so tightly I couldn't politely pull away. "Do you want to see my eye?" he said. One of his eyes was squeezed shut. With his free hand he pulled the lids apart and I realised to my horror that he had no eyeball just an empty socket. I started babbling (still trying to be polite) about how that was very interesting, but I had to go.
Then he uttered the immortal words: "Do you want to put your finger in there?" He was pulling really hard on my hand trying to force my fingers into his empty eye socket.
At this point I gave up on politeness and struggled my hand free (it was difficult, he was really strong) and just ran for it. I could hear him laughing as I ran off.