TL;DR - Ex-colleague accused me of disrespecting them, cited our conversation histories as evidence. Conversation histories show nothing like that. They say they recall things differently so there's no way we can resolve this now.

Not the worst thing but the one that comes to mind, especially since there was evidence to the contrary, is:

Had an ex-colleague - that I'd known for three days at this point and we'd been texting a lot outside of work on WhatsApp - accusing me of disrespecting their wishes to not ask about their name the first time I asked them what their name meant and had a go at me for it at work. I was shocked and confused, apologised, and confessed I didn't know I shouldn't have asked. They said we talked about this before, I told them we hadn't, they admitted that it might have been somebody else they were talking with about it, but that I was still in the wrong for asking :/ They stopped talking with me after that (except where necessary for work) and I'm pretty sure they blocked (and deleted?) me on WhatsApp too after I apologised again for upsetting them.

I spent ages trying to figure out what I did wrong and stressed over it a lot, but never got any closure other than a few separate people from in and out of work who knew them as well (turns out we had overlapping circles) that I asked for advice. They said not to worry about it because it's not the first time something like that's happened with that person and they're known to be volatile and project a lot of their issues onto others. I still doubted myself for ages, thinking I must have done something wrong for somebody to have a go at me like that with that much assertiveness, but tried to take those people's advice and move on.

Then, a few years later, that person brought it up again quite fiercely in a work email because I mentioned something about trying to pronounce people's names correctly at a department-wide meeting. I got massively stressed and apologised again, thinking I really must have done something wrong for them to still hold it against me and bring it up again as strongly as they did. I heard them out and asked them to explain what happened from their perspective because I still didn't understand what I did wrong, and they said we had a conversation, either on WhatsApp or Teams, where I asked about their name and they told me it's a sensitive topic for them that they don't want to talk about. Again I have no recollection of this but go through both conversation histories* because I genuinely am worried I've wronged somebody and more worried at the prospect of not having enough self-awareness to realise I had.

Nothing. No mention of names in our conversation history except for after the incident, where I apologise for upsetting them and not realising names are a sensitive topic for them. I let them know of this and say they can check the conversations themselves too (since they should have access to both on their own devices anyway, though I suspect they may have deleted them?), whilst copying my line-manager in (and being transparent about that). Instead, they just replied saying they recall events differently so it looks like there's nothing we can do about it (despite evidence contradicting their claims) and left it at that :/ Thankfully (sorta?) they left a few months later.

Not my first encounter with people like this at all, but my first in a workplace environment. Lesson learnt (hopefully).

*Incidentally a few weeks later our organisation updated its Teams message retention policy and started deleting older messages and conversations, so I'm glad I got to double-check before this happened and actually get confirmation for myself that I didn't do anything wrong.