I don't hold grudges when it comes to the small stuff in life, and I don't even hold grudges when it comes to the big stuff that someone didn't intend to do. I understand that people sometimes don't know any better about what they should/shouldn't be doing in a situation.
I DO hold grudges (and hold them in a big way) against people who knew what they were doing when they caused problems/harm to someone else; and against people who refuse to question what they did (even if they didn't intend to hurt someone) but who refuse to consider the possibility they were wrong, make an effort to fix any problems they created, and at least acknowledge to whomever it was they hurt, that they now understand what they did.
I can even understand that sometimes someone mistakenly causes so much harm/pain to someone else that they can't face what they did, and can't even bear to try to apologize (often because they think apology "won't do any good at this point"). In other words, I can even understand why some people couldn't bring themselves to even try to apologize.
What I expect from people, though, is this: Just say something like, "I know what happened shouldn't have happened, and I'm doing everything I can to try to fix the mess I created." If there's no fixing it, or sort of fixing some of it; then at least that simple acknowledgment would go a long way to helping the "victim" of some "misdeed"/wrong thinking.
It's a lot easier to get over what someone else has done to us (I think) if we at least know they know what they did and how bad it was. I don't want people wallowing in apologies and shame. As I said, I can understand that people don't always have the best judgment; and I don't think they ought to feel more guilty than they should. All I expect from people is that, "I know how my mistakes caused so many problems and so much hurt in your life, and I know I can't even really see all that problems and hurt you've had a result of my mistakes. I feel horrible, and can't do anything to undo what happened" (unless, of course, that person actually could do something about it). For me, the real issue is whether or not I feel like the other person "has a clue" or not when it comes to what went on. I just need to know the person DOES "have a clue" about his own role in whatever went on. That, to me, is when I'd no longer need to hold a grudge and when I might be able to help that other person feel less bad about whatever it was he did.