What upsets you?
There is a saying I try to live by: Don't do to others what you wouldn't want done to you.
And this is what frustrates me and upsets me, that others who also try and live by that saying or at least agree with it, do the complete opposite.
Not saying that mistakes don't and won't happen, they do and they will, we are not perfect, and that is part of what is beautiful about us humans.
But, when people purposefully do things to others, that they themselves know they would not want done to them, but consciously make the decision to do those things anyway, that is what gets to me, that is what upsets me.