I think I've already replied to this thread (there's a couple comments from hidden users whom I think belong to my old account), but my answer remains the same. It's not so much forgiving them, as it is making peace with what they did to you, or with what those things did to you in the time since. Yeah, it was pretty bad at times, and for a long time I was bitter and I wanted for the worst things possible to happen to them as soon as possible, but later on I realized that feeling that way brought on so much negativity that it was doing me more harm than good. Eventually I learned to just let it go, and focused on things that are actual priorities in my life and that can't depend on what they did or didn't do. It's important not to dwell, and to just live your life the way you want to live it.
I actually came across the guy who was the worst of them all a couple of years back. I remember him tripping me when we were taking a shower after gym class, 5th or 6th grade. I fell on my arm while completely naked and almost broke it. About 20 other kids were staring at my naked, chubby body. Could barely move my arm the rest of the day. He looked miserable when I saw him. Part of me wanted to feel joy in that, but I was already quite advanced in my little phase of letting go of all that dead weight.