I feel like a disgusting person for past things I've said.

There was a time in my life (In my mid-teens, about a decade ago) where I went through an extremely dislikable, narcisstic, nihilistic, unkind phase. In school I used to be cold and mostly unapproachable. But even worse was how I acted in some of my online personas at that time. I used to say some truly awful things to random users, I was so desensitized due to the large volume of toxic behavior on these places already, that it just didn't even occur to me that, -yes, there are REAL people behind those other online usernames, too. Sometimes I used to say offensive things just for reaction, but there was this one time where I 'hoped' something really cruel would happen to someone over, in retrospect, a truly trivial argument.

I dunno what happened to my moral conscious at that time. There was no reason for me to go there.
No one ever, EVER deserves that, and even if I didn't REALLY mean it, for me even to JOKE about something so terrible is appalling, really. From what I remember, there wasn't a response from them after that. It's possible I may have really deeply messed them up on that one. Maybe they didn't give it a second thought, because I was just some random asshole on the internet who they didn't know. But I don't know. Everyone takes things differently, as I've had things wished upon me as well, which I just take with a grain of salt, but I'm aware it is not the same for everyone.

As I've become older, I've LONG since abandoned that schtick (it only really lasted a few months) and I've actually become very sensitive and always tried to be kind to people irl. Just recently the memories of some awful things from back then started hitting me immensly, and now I wake up every morning with guilt-chest pain. I deserve it. I've even been telling myself that if I were to get a heart attack from intense guilt, it'd be deserved, even if I die. Guilt just seems to get worse as time goes on, and ironically it may just serve as my end.

As much as I try to tell myself "I'm not that monster anymore, I was just a teen etc", and I would NEVER say cruel things to people anymore, even anonymously, I can't let it go. I may never let it go. I've been feeling socially distant again lately just because I feel like all the people who think of me as a good person have no idea how truly awful I used to be.

I'm so sorry to everyone out there who was offended/disturbed by what I said back then. I'm. so. sorry.

You were a teen and, in truth, I respect you for recognising your past behaviour as abusive and apologising for it - because literally millions never do and never will. I do think the internal can bring out the worst in people. I also think it's pretty unlikely you did much more than ruin people's day (not that that in itself is okay, of course). I've had people online tell me to kill myself (ironically over being bad at an online game not about any of the stuff I actually feel guilty about) and it has hurt, but there has also been a certain detachment. I think doxing goes further and certainly the sheer relentlessness of online abuse can wear people down - so maybe donating to an anti-bullying charity could help.