Shoulda Coulda Woulda

I have been puzzled by several people's notions of regret and reconciliation with the past. Though nothing has recently incited this posting, I feel I've digested the matter sufficiently to venture an opinion. There are those that say they do not regret any of the things they have done in the past because there's no point in dwelling on the past, or that if it wasn't supposed to happen it wouldn't have, or frequently that they do not regret because the experiences made them who they are today. While these are all well and good means of coping with one's ignoble past deeds (and I believe any rationalization that works is better than sullenly obsessing over one's mistakes) I wonder if people apply that type of reasoning beforehand. Something along the lines of foolishness begets wisdom, which I can hardly disagree with since I know several people with colorful pasts with a wisdom beyond the ken of my own stuffy self. That said, such wisdom does come at a cost of happiness and if the idea of regret even enters one's head it was probably not something altogether pleasant.
But just because someone went through such an experience does not necessarily make them wiser. There are some who do knowingly things against their better judgment and later claim the ordeal was worth it because now they know why it was a bad idea. This logic baffles me; it's as though they decided to hit themselves in the face with a hammer knowing full well that common knowledge says that's a painful experience, then after hitting themselves in the face with a hammer declare that the experience was worthwhile because now they know exactly why people always say, "Don't hit yourself in the face with a hammer."
There's also the issue of what everyone else will think about them. Now common belief holds that we shouldn't care what everyone else will think about our actions. In the literal sense this is true; we shouldn't worry what everyone will think, but I have yet to meet a single person who does not alter their behavior based on what some will think. At any rate, whether or not you decide to feel (or at least tell people that you feel) regret is contingent on how you think people around you will react. In the realm of, say, sexual experiences, if you knowingly enter the situation and can reasonably expect the experience to ultimately be negative or humiliating you have two options. You can either regret doing something against your better judgment and have people think you're a fool for doing it in the first place (as I admittedly just did in the previous paragraph) or you can adopt the "No regrets!" attitude and have people think you're either a slut or a womanizing pig. So the choice ends up being, do you want to be thought of (by yourself as well as others) as stupid or rakish?
Moving away from specifically sexual regret, people still have different concepts of regret, or at least different from how I would qualify or define it. I think people who claim they have no regrets think that it means constant sullen brooding over some past action they wish they could have done differently. I would qualify regret at its most basic as when you wish you could have made a different decision given the information you had at the time (hindsight is always 20/20, after all). For example, I sometimes wish I had made more of an effort to have a more socially eventful freshman year of college. But had I had a really great time that first year, I would have likely felt I had too much to lose by leaving the country for a year. So in that instance, I do regret not doing something even though that nonaction ultimately resulted in the amazing experience of studying abroad. On the other hand, though, doing something like being needlessly mean to someone at some point ultimately made me the person I am today. But if I hadn't done that would it really have made such a profound difference in who I am? And if it did, who can say whether it would have been an improvement or not?