I remember a day at the office of a former job; there was one guy, the "chief developer", technically solid, but he was a pure a**** when interacting with others; it was quite known that he was a "difficult person".

One day, I opened the door to another floor and he approached the opened door: I saw him with two things in his hands: the one was a Leitz folder, and in the other hand he had a cup of coffee - so full that the coffee was kept in the cup already only because of the surface tension of the liquid.

I held the door opened, looked at him, a small smile and noded - he didnt show any reaction (not even think of a "thank you" or similar)