I don't mean to be dismissive, but I really don't understand what you're trying to say. My understanding is that we are talking about face-to-face interaction with a clearly frustrated person. Why wouldn't you know they were frustrated?
>some times people are having a really bad day for reasons you can't see
It's not clear how you know someone is having a "really bad day" when you explicitly rule out knowing the reasons why the person is having a really bad day.
Maybe they told you they are having a really bad day? That is fine and fairly easy to empathize with.
Maybe you are just assuming someone is having a really bad day because of how you perceive their actions?
