There are just somethings in this life that cannot be avoided. Things like being hurt or offended by people. First of all, we must know that nobody under the face of the earth is not perfect. We also may have hurt or offended someone either intentionally or unintentionally.
The problem with most people is that they are too quick to point out other people's faults but fail to see their own faults. If we expect God to forgive us for every time we fall short of His glory then we as well should be able to forgive people without any restriction.
Even if someone offends us and it's their fault it should not stop us from forgiving. The disadvantage with holding on to grudges is they keep us in one spot and hinder us from moving. The Bible encourages us to move on.
Whatever occurred in the past should remain there. We shouldn't bring them along with us in the present. Offenses are part of the things were must face in life. If it were to be in our power to prevent them from occurring then we would. But we can't. But what we can do is to let go and forgive.