All righty, this is gonna be a long one, but I promise it's good. This didn't happen to me exactly, but I was directly involved, and it almost scared me away from online role playing entirely.
It was an interesting time in my life. I was barely an adult, and confused about Gender, and was just starting to use RP to figure things out. At the time I was playing an MMO called Champions Online, which had just gone free-to-play. This was kind of a bid deal for me because I had quit the game a year before because I couldn't afford the subscription fees. Now, before this point, I had never even considered roleplaying in an MMO, and with the huge amount of character customization available right out the gate, I was hooked. I got all the RP mods and quickly made up my first RP mmo character, Kendra the trans girl drow. After a few days of hanging around the unofficial RP spot, I met a couple of people, roleplayed with them, and got myself invited into their RP guild. So far so good.
I roleplayed with these guys for a few weeks, maybe about a month or so, and there were a few red flags - for one, in that guild you weren't allowed to have other characters in other guilds, which I thought was strange. There was also this annoying focus on the guild leader's character being over powered as hell which caused me some annoyances with some of the adventures I was working on, but it was fine. My character even had a boyfriend, so that was cool, too! I was just starting to get comfortable with roleplaying a trans woman, and decided to make another character.
This other character was Casey, a female red dragon locked in humanoid form. She actually had two forms - a cool thing about Champs is that you could make I think up to three outfits and swap between them. Casey's first was her human form, literally just a punk girl with red hair. Second form had dragon wings, and third was full scaily. She had a bad temper and was usually pissed off because she had been locked out of her true form and power and was forced to live as a mere human. Also, for story reasons, she had to work as a waitress at the RP bar, and I used to serve people with a huge frown on my face and make snarky remarks about them... good times. I miss Casey.
So the guild master's character was in a marriage with another guild member's character. Pretty normal, they had been roleplaying together for a while, and it's all just a game. It's just RP, right? Surely these were reasonable adults.
So Casey, my alt character, meets... can't remember his name, like, Spiff or something, who happened to be the guildmaster's character's hubby's alternate character. Long story short, Casey and Spiff do the dirty, and I realized I am VERY much the girl in pretend relationships. First erp for the win, and I got to do it in Casey's scaily form, so also my first scaily erp. It was great, we were both mature, it had a semi-romantic feel to it but was also a one-night-stand with a possibility of more, that kind of thing.
Fast forward, Casey gets involved with an out-of-guild story line with some dude who wasn't as good as Spiff, but still pretty good, and out characters are having a heart to heart. Meanwhile, my guild master is playing a new character, whom I remember being a female-to-male trans character, because it was his first trans character and he thought I would be a good teacher for some reason. He's bored, and he asks me if he can hang around and listen to our rp. It's fine with the other guy, so I say sure, why not, and continue my in character heart to heart.
This is where things go sideways.
While pouring out her emotions, Casey makes a comment about F*****g Spiff, just to feel something, and then I get a PM from the guild master. "Did you say Spiff? As in, my husbund's alt?" Foolishly, I didn't think anything of it, still believing this all to be make believe and all. So I say something like "Yeah lol." Suddenly, I am absolutely bombarded with PM's, all about his relationship with Spiff's main character, and "how could he do this too me?" and "He ripped my heart out!" and "How could you cheat with my husband!" and shit like that. Then, he goes on a rampage, tearing the guild apart and lashing out at his husbund who, as it turns out, also thought it was a pretend relationship in a videogame.
The guild completely fell apart after that, and a few of the guild members blamed me personally, as if I was some kind of home-wrecker. One girl, whom I thought I was friends with, even told me that it was well known that the GM couldn't differentiate between real life and roll play. I ended up losing a lot of friends all at once over that. And by the way, I was NOT nice about it. I called out everyone and anyone who was knowingly playing into this guy's delusions and attacking me, and things got so bad, I quit Champions Online forever. Which is a shame, because it was fun as hell.
And that is my worst RP experience ever.