How do you deal with friends who harsh your buzz? E.g. you're relaxing on the sofa on an evening, maybe with other mates. Your flatmate returns home all tightly wound and stressed from his job, which is much more high-powered, better paid, and more serious than yours is. Just his anxious presence is enough to kill the relaxed mood of bonhomie in the room.
I normally offer them a beer, but this doesn't always work.