It doesn't seem that you are really hearing what many of us have said because you are still using terms like "these people." Who are "these people?" What makes them "these people?"

Clearly, the strangers who did not include you in that conversation are not the actual parents of the children who are bullying your son. After all, they were strangers; you don't know if they even have children! I also doubt that your co-workers are the actual parents of the kids bullying your son. If so, I would hope that, since you work with them, you were able to pull them aside and talk to them for the benefit of your son (as opposed to worrying about your own social issues with them). However, what it seems like is that you have just decided that anyone (including strangers) who does not invite you into their circle with open arms is one of "these people" who was a bully as a child, is now a bully as an adult, and is having bully-children. Who's the one here making judgments? For all you know, the reason those people in the parking lot did not include you is because they were talking about a divorce, an illness, a problem with a child, a romantic escapade-- or something totally inappropriate for you to be a part of. That does not make them part of the "grown-up version of bullies." Maybe, if you stopped referring to everyone as "these people" or "people like this," you would be able to stop making sweeping generalizations and work on building individual relationships with people. Rather than trying to insert yourself into existing groups (which isn't working out), you could try making one-on-one connections with people and make some friends that way. The people you see talking in groups are friends because of individual relationships they have with each other; they're not just a travelling pack. If you had individual friends, then you'd have meaningful relationships in your life and people to introduce you to others or include you in groups.