Obligatory "not today" disclaimer: actually fucked up over two decades ago, but found out today.
At the dawn of theinternet, I made an account on imgur. I figured (correctly) that I wasn't going to use it often enough for the username to matter much, so I just went with the first part of my email adress and a number four times.
Turns out that there is such a thing as nazi number code and it's never a good idea to use an even number of 8s for usernames when you're not a nazi.
TL;DR: Didn't know about nazi code, accidentally selected an imgur username ending with the equivalent of a double Hitler salute
I did the exact same thing. I've been using the name for decades and recently found out about this. My initial reaction was, "Fuck them. I've had this username for years and I'm not gong to change it just for them." Unfortunately, while I know that it isn't related to them, no one else does. It sucks that they get to take possession of it like that but I prefer the inconvenience of changing usernames over the mistaken association with that shit, so I changed the ones I could and abandoned the ones I couldn't.