One final point on forgiveness I didn't manage to sneak into an earlier post:
For fallen man, Christian forgiveness is hard.
It's hard because it takes humility and meekness to renounce a just debt. It takes an uncomfortable degree of self-knowledge to recognize our own need to be forgiven. It takes a robust faith to leave all judging to God. It takes, God help us, practice to love our friends as we love ourselves, to say nothing of loving our enemies. And all this needs to be done under the one organizing principle of human acts: to love God with all our heart, all our soul, all our mind, all our strength.
But it's also hard because, unlike clemency, forgiveness is an interior act. That means there's nothing external and irrevocable you can do to forgive. If you're lenient toward someone, there's firm evidence of your clemency, and you can't later on not have been lenient. If you give alms, there's physical proof of your almsgiving, and you can't (practically speaking) get your money back later.
But to forgive someone, in particular someone who doesn't ask you for forgiveness... well, how do you actually do that? You can say, "I forgive him," but unless you're God your words do not create the reality they signify. You have to somehow or other... just forgive him.
Of course, Christian forgiveness happens by grace, and becomes a virtue by practice, so saying, "I forgive him, the miserable rat," is a good way to start, as long as it isn't where you stop. A prayer like, "Dear Lord, please grant me the grace to desire to pray for the grace to desire to forgive," may be in order.
And once you've forgiven someone, what's to stop you from unforgiving him later? Nothing, as far as I can see, except grace.
Christian forgiveness, then, demands all sorts of prior virtues and is given in an intangible and so-to-speak insecure manner. No wonder Christians are so bad at it.
And how do we get better? Well, have you tried prayer and fasting?