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
United States federal ambulance regulations got the unfortunate designation of "KKK" (edition *a, b, c, d etc). So now when I search for information for both compliance and product purchasing I have to figure out a way to enter things into a search engine that won't get them blocked at work or get me on a list I don't want to be on. Recently the term triple k has been usable but a lot of products still start with the three letters and then their model number, worse yet many have a space between the three letters and the number.