Here's a thought related to both the original post, and what happened. And it's not a reflection on either of the people involved (OPs colleague and the poster of the message that upset, I don't want to open that discussion again). It's a bit of self reflection, and though we're all different perhaps it's something a few of us share. So here goes.
I've noticed that I REALLY struggle with these situations and I feel that maybe the OP's first post had a similar situation. My partner says I don't like confrontation, which has some truth, but it's this particular kind of confrontation where I feel exposed for having social deficits. So things like the "erm, what are you doing?" or "how dare you?" knock my legs out from under me especially if it's accompanied by aggression, anger and confidence. My first reaction is "Oh ****, what did I do wrong?" because I've always been aware of this deficit in social ability. So my first emotion is stress as I assume I'm at fault, followed by a need to put things right and return to some sort of harmony. I don't know if others relate.
And it echoes on. I'll ruminate, self-reflect, review what happened to sort out the confusion it brings. It's quite black and white thinking in some ways. If I realise that I am indeed the one at fault, that sticks, for a long time, perhaps decades. But if I logically come to the conclusion that actually, no, that wasn't on, I get resentful but STILL won't make my feelings known because I'm fully aware that the other person is skillful is this area and will probably find a way to humiliate me.
I seem to be missing something that allows me to navigate this type of thing. I watch situations where people do the things OP mentioned in the first post and I think "I wish I could do that" in some ways. Things would be easier if I had that self-belief. But how can you when you know you're missing a skill that others have naturally? Personally I feel like I'm vulnerable in these situations and I don't like that one bit. Does this resonate with how you felt in that situation
@mysterionz ? Happy to take this to another thread if not, because it's a problem for me that I would like to solve as I think it leaves me open to manipulation, but if it's a shared problem perhaps we could share ideas for dealing with it?
EDIT: Again, not wishing to hijack, so can copy paste this into a new post if needed (and note: this kind of over-qualifying everything I say is another symptom)