I prefer not to stir up unnecessary conflict. If someone makes a direct attack on me or someone close to me (or make an attack on someone in my presence), be it physically or verbally, then I will stand up for myself (or the other person), however if they can keep their own personal feelings in check, then so can I.
I tend to stay clear of people I don't like if I can help it, but whenever I am forced to be in their vincinity (whether it is working with them or attending some social gathering where they are present) I prefer to keep a polite tone, because the day tends to be more pleasant if we can just manage to get along for however many hours we need to interact. I tend to know where I have people, if they are people who like/accept me, tolerate me or cannot stand me. And as long as I know where I have a person, then I am perfectly capable of filtering the things said to me or in my presence.
There are people who have hurt me (especially people from my school days) and if I ever were to encounter them, I'd probably just ignore them as much as I can. Because thing is, if those people have grown up and are feeling bad for the hell they put me through, I honestly don't feel like listening to their apologies, because a couple of words aren't going to undo the damage they did. And if they don't feel bad, then I really have no interest in being in their presence whatsoever. Thankfully I've managed to mostly stay clear of my past bullies (it helps to have moved to a completely different town and only coming back for 1-2 weeks at a time), and I hope to keep it that way. I don't think I'd confront them about it, I just prefer to stay clear of them and instead seek out those few individuals who didn't make me go through a living hell.