This thread is actually very upsetting to me (ironically, I suppose), and I think that it is because those that are laid back generally do not understand the problem. I want to know how not to get worked up, and the most up-voted and common answer is "just don't". If it were that simple, I wouldn't be here.

Can I please give a more specific example, that someone can address with a more specific solution? Here is an anecdote from not long ago: I was at work sitting in on a team meeting. One of our new hires presented her work for the first time. It happened to be on a project that I had been working on and been told to abandon by my boss. The things that bothered me: This person was presenting all original work, including work that I had done years ago, but she re-did completely. Clearly, my boss never informed her that I had already started on it and she could have come to me for what I had so far. I felt like he didn't give a shit about what I had done before - either forgetting I had done anything or not trusting my work. I got upset during this team meeting, telling her during her presentation, "I know the answer to this question you claim youcan't figure out, because I was on this a while ago. If I had known you were on this now, I could have told you." It ended there, and I apologized to her in private immediately after, which she accepted and we were okay but not great. But my momentary lash-out caused her, my boss, and everyone sitting in on the meeting to completely lose their respect for me. I have noticed it considerably, from people stopping inviting me to lunch with them, to eventually me going entire months without any interaction at all in the office. Prior to this, I feel like I had pretty adequate amount of respect and friendship there, so I see that as evidence I'm not a terrible person on the regular.

Now, laid-back people, I implore you to please tell me how I should handle this within myself. I am very upset still even though this all went down nearly a year ago. I am upset with how I handled it, and with everyone involved for how they treated me afterwards. I know I cannot change the past; I'm over that part. My ongoing anger is toward people who continuously judge me, i.e. literally everyone.

This isn't something that "just doesn't matter". It affects my job and self-esteem on a regular basis, so it does. Additionally, I have tried to be productive about it and re-insert myself socially, but I am most definitely being shut-out actively. So nothing really fits with any advice here.