If it's someone completely random, I'll give them a reason to pick a fight with me, can't go around playing nice guy forever. If it's a friend, which in my unfortunate case, I try to solve and it ends up blasting way out of proportion- I mean, I give only one chance, after that, it's pretty much the highway. As for your question: Well, it takes a lot for me to speak out of line, or give my "true" piece of mind. They most likely deserved it for pushing the situation that far. I don't speak on impulse, and I try my hardest to be rational. Sadly, my nasty habit is holding grudges that could most likely last a lifetime, but once I'm convinced a person will not change, or whatever the case may be, I'll never associate with them again. No one needs a hindrance like that. I'm all up for mutuality and all that good stuff, but you have to show some respect to receive it. Disrespect flows within the stitches and seams of this place we all call home. Everyone has their own way of handling it, whether being in denial, accepting, or flat out condemning the "offender."
Usually, no, I don't regret things I say to people online. Because first, like you mentioned, the past is the past, what's done is done. You can't do anything about it...unless you have a time machine (lol). Second, the person I argue is online (unless the person is someone I know face to face, then it's a whole 'nother story). Therefore, since I don't know that person well, I don't care what I really say because at least I know I won't see him/her in person and waste my time continuing the argument. And third, from reading your situation, the person might have done this multiple times? So if it was me and I had some sort of similar fight like that and did what you did, then I wouldn't regret it because the way I see it, if the person did it here and there, then that's fine. But if it becomes repetitive, then someone has to lay down the line. Because there is a point where you should understand the person's situation and there is a point where it's too much and you have to put a stop to it and have the person realize what they are doing is not ok.
I hope this, or most of it, answer your question...
On another website, sadly long gone, a fantabulous and extremely vitriolic argument broke out about who'd win in a fight - Jesus or Hitler - and the replies added in that case even led to the police being called and there being a whole investigation into the thread.
I was supposed to be moderating it, but after a few days I just gave up.
Yeah, that happened to me several times. Like, they wouldn't let me reply back, but then, they would make a new account to say the last word, and then block me on that account again. Like the hell?? Obviously that person got some spare times on their hands to do that, lmao ; but they claim they don't give a crap, when in reality, they actually do.