I don't hold grudges. What I do is remember past behaviour, predict future behaviour on evidence of behaviour seen, and make an informed decision on that information.

For example, someone lies to me. I wonder now if the next thing they say is a lie. A few months of truths later, lying is not considered much. Some consider that holding a grudge for a few months - but I am not rude to the person, I just query information given. If it were a big, earth-shattering thing (eg "I would never sleep with your husband") that was a lie then I may well not be friends any more - is that holding a grudge? Would my reaction to my husband be grudge-y?

I don't hold a grudge against my mother, for example, for the way she brought me up. But she is going to be warned next time I see her (next month) that I have noted this year she has started to do similar things to Liebling and if this continues we will not see her beyond this year. It is not holding a grudge to say "I dislike XYZ behaviour, you did it before in this instance, don't do it again." It is wanting my son to grow up abuse-free and the "right" of a grandmother to see her grandson does not include her abusing him. Not a grudge, honset! If it were, I would not see my mother at all and would find a way to make her hurt for it.