I don't think it is worth being angry for years, but if the moment appears... A few years ago on Facebook I friended an old school pal who is now an occasional theatre player and had always got on well with him. He is friends with another school pal who I did not get on with at all well at school. Dan would taunt me endless about my accent, physical build, mannerism, lack of friends etc - you get the picture and being of slight stature there was little I could do. Fast forward 30 years and the actor friend had a show coming up so I wished him well by saying "Break a leg" on his Facebook page.
To my utter amazement Dan added a comment along the lines of "Oh yes Pat, good luck, what ho, kiss kiss Hope you do well, love you" and so on, exactly how he used to mock me all those years ago. What did I do? Well I deleted my comment so it appeared as tho Dan had promptly wished Pat a very gay good luck. Pat then replied "Oh thanks Dan, kissey kissey to you too", etc and a very gay reply at that.
Browsing Dans FB page a day later and I saw a post about how he thought it was about time he lost weight and how he couldn't believe anyone could hold a grudge for 30 years. Not long after he pulled his FB page. I hadn't held any such dislike for him but found it absurdly amusing that he had relapsed into his school bullying with the first sight of my post, so I kept my cool and thought of the most vulgar way I could manipulate his riposte. Which I thought was fairly cruel - but worth it.