Honestly I’m not good at guessing what kind of mood a person might be having by looking at their faces and gestures. But I think I’m pretty good in detecting the mood in a particular setting: when a student comes into my classroom.
I would know if a student which I see twice a week just had an exhausting day at school as they would often yawn and put on a bored-looking face and when I asked a few questions, some of them would start telling me all sorts of problems they had had that day.
But I could also notice whether someone had been having arguments with their parents of boyfriend/girlfriend or when they had just achieved something. I guess that even if you are not a psychologist, a mood radar is an inherent skill that you can opt to use from time to time.
Just my two cents and the first trial to the Daily Prompt. ^^