For me personally, since wildcat hit the nail on the head when it comes to forgiveness.
There isn't a whole lot I won't forgive.. but there is plenty I will never forgive entirely, and there is still more I will never forget.
Rape is unforgivable. Raped someone recently? You're not on my friend's list.
You murder my family, consider yourself off my Top 8.
Things of magnitude like this are black and white for me..
..But you do provoke my thought process on smaller things.. Like.. when someone lies to me something dramatic.. do I ever really forgive them? Does the whole "Forgive but don't forget." philosophy count? I mean, I probably won't trust that person as far as I could throw them.. but it's not enough to make me burn the bridge yet.
So I guess unforgiving acts, for me, would be something severe enough for me to never want to talk to you again.