Ever since the early 2000s, when I was using Linux IRC clients which would paste anything you had in your clipboard when pressing the middle mouse button, I have been scared out of my mind that I would one day have copied my sensitive.txt file content's and accidentally pressed the middle mouse button, causing many linebreaks which were interpreted as "Send", flooding some random IRC channel with my private information.
As far as I know, it never happened, but it came damn close many times. Middle-click-paste was an idiotic invention if you ask me.
The same goes for posting to Stack Exchange. I always type my stuff in a different window and only copy and paste the full text once I'm done. Of course, I always make sure I didn't paste the wrong text before hitting "Submit", but what if you accidentally didn't? Once you have posted it, it takes mere seconds at most for bots to grab that content and supposedly store it indefinitely.
In such a situation, or the one I described with the chatrooms, there is nothing you can do, is there? Just leave in shame and never come back, desperately trying to change your passwords to any accounts that were pasted or trying to brush it off as a "social experiment"?