A stranger fixed my bike chain in the rain and refused to take anything

Biking home yesterday in freezing drizzle, chain came off and my hands were too cold to do anything useful. An older guy walking his dog stopped, handed me the leash, fixed it in about a minute, and wiped his hands on a tissue like it was nothing. I offered him money for coffee and he said 'just do it for the next person'. What's a small kindness from a stranger that stuck with you?