This happened to me yesterday. I was sent into a supermarket to buy some milk and fruit juice: four items in all. The particular supermarket did not have a ‘basket-only’ aisle, and the queue for the only self-checkout was enormous, so I joined a queue of people with full trolleys - maybe 50–100 items?

We got to the point that there was one man in front of me, with his 100-odd item trolley and, while the person at the till was still unloading their items, he turned to me and said if that was all I had, go in front of him. I thanked him and moved in front. About two seconds later they announced another aisle was open, and he got served immediately.

I liked that!