I have two, but I can’t choose.
Once when I’d just been diagnosed with epilepsy I had a seizure out of the blue on a bus alone with Dd and a woman jumped out of her seat, sat with Dd and sang with her whilst making sure I was ok and making sure Dd wasn’t panicking.
Second when Dd was days old I’d taken her out for the first time on my own, and we went to cafe for coffee and I was breastfeeding Dd. A woman came over and said you’re doing great. It was a second of interaction but to a first time mum I felt incredible after that.
Also anyone who waves to dd from a bus/tractor/train/bike!