If you're reading this, you've probably said something awful to someone in the past, whether it be a passing comment that you've come to regret or outright bullying that could have had a lasting effect on that person, it doesn't matter. You should go and apologize to that person.
I don't care how long ago it was. The person still probably remembers, and now is your time to make peace with them and own up to the fact that you did something wrong. If it was five or seven or even 10 years ago, that is okay, too. Now, the person probably doesn't remember, but if it is something that is really bothering you, you should apologize anyway.
People are mean, it's true. Honestly, I think it's human nature to be judgmental and not always realize the impact that you have on other people. You never know how much one statement will stick with a person and possibly haunt that person for the rest of his or her life. Or maybe anytime someone brings up something that relates to that statement, it'll just open up old wounds.
Recently, I had a person come back into my life who I thought I would never hear from again. We had a bad falling out and just stopped talking after almost two years of knowing each other. She messaged me to apologize for what she had done and that she was working to fix herself and that she wanted to come back into my life because she still cares about me. And that hit me pretty hard because just before I came to Orlando, I had the worst falling out I may ever have with a friend I had known since 5th grade. We would fight on and off for about six months and it finally ended in the summer with her sending me many reasons why she hated me and how I was the worst person she had ever met.
That hurt. A lot.
Which is why when the other person came back and actually apologized and felt remorse for what she had done, it hit a soft spot with me. If she can message me almost a year later and say I'm sorry for what I did and it was wrong, she must have been thinking about what she had done a lot during that time. And that other person was never able to do that so she must not have really cared about me.
Being able to own up to your mistakes really puts life in perspective and makes you realize who the people are that you need to keep around. So even if you don't want to be friends with that person but you still feel bad, just go ahead and tell them that you're sorry, because, in the long run, it'll make you feel so much better about the whole situation.