Perhaps a mean comment that you would want to take back and apologize for? Or something that you maybe wanted to post anonymously but didn't, and later came back and saw that it had already received a lot of attention.
I personally do have something I'd say sorry for to some people. I remember I once slutshamed a woman here and I still don't even know why.
I have posted over 33,000 opinions so of course there are some I am not proud of. My hall of shame includes probably being wound up by outside influences but losing my temper a bit with MRAs and White Pride questions, I was unnecessarily sarky when I should have avoided question. Also a couple of times with repetitive and dick size questions. Yeah I think that is main thing being sarky when I should have avoided question. I have blocked once to get last word in an argument. On personal side maybe a couple of times revealed too much but overall I would say I am ashamed of maybe only about 0.5% of my answers.
I can't think of a time where I insulted someone. I'm generally too cautious for that.
There are some things I regret though. Sometimes you get involved in conversations with people who turn out to be complete tools. Also some questions I've asked got poor answers. I remember one question about improving social skills and a response was "Don't bother. No one wants to know you." I was anon ffs.
Also sometimes I try to talk to people who have assumed too much too quick and it's just a waste of time and energy.