I once had an old lady come up to me and, completely unprompted, give me a lecture on the difference between the German words "kein" and "keine" as if I had mistakenly used the latter instead of the former. She was in a heated argument with someone else at the bus stop but she saw me approaching and ambushed me with that lecture as soon as I got there.
She did not stop arguing with strangers the entire time I was within earshot of her, which was quite a while.