Thou shalt not avenge , nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the LORD. — Leviticus 19:18 (KJV)
Grudges are always more destructive to the person holding them than the person who's a target of them. Which is why it's not terribly smart to hold grudges, and you'll be a lot healthier and happier if you heed Holy Scripture and just let things go. Bygones, and all that.
But "letting go" of those you feel have wronged you is not always an easy thing to do. Thus a grudge by inaction becomes revenge in action.
Humans are hard-wired for revenge, and modern humans have elevated it to an art-form. When we're not seeking revenge, we're enjoying it as entertainment. This is not something we're proud of. Our aspirations are so much higher. But you can't fight human nature.
And by "you" I mean "me."
I expect so much better of you.