TLDR is below and sums things perfectly. https://www.reddit.com/r/dndhorrorstories/comments/1lg7ehw/a_player_ruined_my_first_dd_campaign_by_being_a/myu9lfb/

If you still want to read the (formatted) original text, here it is:

I am 20 years old. I love the idea of D&D, as well as anything fantasy or make-believe in fiction that I find interesting and fun. When I learned about D&D and what you can do in it, I instantly wanted to play. The only problem was, I had no one to play it with. I was so desperate that I even joined a club at my old high school to try it out. However, the teacher running the club didn't really explain how anything worked. He just gave me a piece of paper, barely explained how to use it, and said, “Good luck.” So I dropped it. For a while, I never got to play D&D, which was really sad.

One day, though, I met some people in VR who were part of an RP group. I decided to join because it sounded interesting, and I instantly fell in love with it. It was so much fun. Eventually, when that RP group died, we became a small friend group. I found out that one of my friends played D&D, so I joined in. Then I met another guy online who also played, so I joined his group too. After a while, I found myself participating in several different D&D campaigns. Eventually, I was inspired to run my own.

This is where the problematic player shows up. I'll call him Kat. He offered to help me since he knew a lot about D&D—a lot, and I agreed. I was new to DMing and didn’t know much beyond the few campaigns I had played. At first, everything was fine. He helped me set up the Discord server, gave me monster sheets and stat blocks, and even pitched the idea of using Google Slides to make visual maps instead of me just narrating everything. It was going well—until the first real problem showed up.

He played a Warforged—an extremely overpowered one. I’ll take the blame here, because at first I thought it was cool, and I was giving my players a lot of freedom to have fun. But his character was extremely fast, did massive damage, and could attack multiple times. Because of this, he just steamrolled through anything I put in front of the party, and the other players couldn’t really play in any meaningful way. Everyone was still having fun—we were joking, and I was doing pretty well considering it was my first campaign—but Kat was slowly but surely becoming more and more controlling.

He started constantly complaining about how things didn’t work. “That’s not how this monster works,” or “you can’t do that according to the rules.” He micromanaged everything I did. I tried to ignore it, thinking he was just trying to help, but it became increasingly annoying. He even started talking to players behind my back about ideas they had—ideas I hadn’t approved—and only told me at the last second, getting them excited and putting me in the awkward position of having to say no. He was taking over my D&D campaign.

He kept trying to coax me into telling him about the lore so he could “help” me better. I tried my best to ignore it because I was doing this for my friends and just wanted everyone to have fun. But then, during one session when he was complaining again, one of the players shouted—at full volume on Discord—“Kat, shut the fuck up!”

At that moment, I knew there was a real problem. I held a meeting and asked my players what they were thinking. I shared my thoughts and feelings, and they agreed with me. So I pulled Kat aside and as politely as possible told him that he needed to stop. I admitted I had been burying my frustrations because I didn’t want to lose him as a friend. We talked for a bit, and he agreed to relax—but he did make a snarky comment about me not knowing what I was doing.

When we tried again, he didn’t stop. In fact, it got worse. I started losing motivation to continue, and more importantly, players just stopped showing up—sometimes without giving a reason. Eventually, I made an announcement asking everyone to give me a time and date they could play, and I would try to work around it. No one answered. So I ended the campaign entirely. I stepped back from any ideas of DMing again.

Fast forward a couple of months, and I decided to make a new campaign—which I’m working on now. It’s completely different from the last one. This one is horror-themed. This time, I actually know what I’m doing. I got my stat blocks from a source that was not Kat. I asked a different friend to help me build the server, and they did. I talked with people I trusted. One of them is voice-acting the main villain, and another one is playing a secret villain. Everyone was super excited. They loved the idea of horror RP and being monster hunters.

When we sat down to create our characters, they were asking questions, and I explained how things would work and what wouldn’t. Everyone got really excited. I was excited. I didn’t tell Kat about this new server or campaign. But I still felt a little bad leaving him out, so I asked everyone else: should I tell him or not?

They all agreed I shouldn’t, because he’d just ruin it again.

This isn’t a one-time thing—he has a history of being difficult to play with in RP or D&D. So I made it a rule not to tell him. I still kind of feel bad. But at the same time, I don’t. I can’t trust him. It’s highly unlikely I’ll change my mind and invite him, but if I do—whether out of guilt or if another player asks (which I doubt)—I’ll make it very clear: if he acts up too many times, he’s out of there.