Like many have posted so far, I do not show much emotion. I come across really calm and most of my strong feelings stay within. But, certain things on rare occasion cause me to have a tear or two in my eye. It seems to be always either when someone does something totally nice, inspiring, unexpected and/or outside the typical goodness norm, in a very caring and unselfish way; a really good deed to a really disadvantaged or victimized person without wanting the attention for it, or when someone says something about me that I wished my parents or others had said to me.
Thus, in my case, I think I need to see something that is very jolting, like in terms of much compassion shown, and if I sense much understanding, see sincere complement that I always desired but never received before, or if I saw like some great deed or effort outside their usual ways or that I felt showed extreme kindness to unimaginable levels, and/or if the sincerity shown I sensed was to extreme levels. Those situations may be needed to get any certain feelings like any crying out of me, and as rare past experiences showed..
It could be either a situation like where a very abused child, animal or adult found a very safe and comfortable home, with them experiencing finally some stability or happiness there, or like if someone pulled me aside and said, "You know, you seem like a great dad for all you do" or "I wish I met someone as nice and caring as you." I mean, I like very happy/unexpected endings and when others appreciate others' selfless great efforts and sincere kindness towards others. It makes me sad when persons take all that for granted. So, when I see someone sincerely notices it and calls attention to it on rare occasion, it can bring a few tears.
So, although I have the ability to empathize with most persons, I tend to on rare times let out that emotion for those big helpers and victims, usually for cases I most relate to, like if those situations seem similar to those rare times in my life that one or more reached out to help me, and if they seem similar to the abuses I faced or where more harms I sense occurred, but with some happier ending. It makes me really happy for the giver/helper and receiver/victim in those cases I empathize with or relate most to, and when others focus on complementing those who go out of their way to be really good persons or who just always seem to have been that way.