I met JA at one of the C3 conventions . he's an extremely charismatic guy. you get sucked in. But then after a while he started to behave very badly towards one in the group. Shaming her and being a jerk in general, but with a smile. I dont know if everyone got what he was doing because it was delivered in such an underhanded way. I couldn't stand it and walked away, and I still regret I didn't tell him to shut the f…
A fundamental lesson that I came away with from the whole mess was that a measure of a person is how they treat others. You can allow for some variance in temperament, or the stress of a situation (I have flamed people back in the day), but as long as one acknowledges overreaching, or the wrong of getting too personal... it shows a basic fundamental respect for other people. The psychopath I had to deal with had none of that - it took time to gather enough data to see through his charming behavior and "acknowledge" whatever compliments he may dish out never quite felt sincere, considering the bulk of his behaviors were essentially bullying behaviors.
As for your feelings of regret, I am there too. I should have been more assertive, in retrospect, to get this person to back down - we were always butting heads in some fashion, but it was more sniper fire-ish - when he did cross the line, a thorough public chewing out (as professional as possible) on Facebook (that was the comm channel he insisted everyone use for business purposes) might have taught him some respect. Or enraged him so much that he would have finally tipped his hand about his true nature. But the group's standard response "well, that's Peter... he really needs to get off social media once in awhile, his dog is sick, his mother just died...." Rationalizations But over time, the cognitive dissonance builds up enough that you can't ignore it all anymore.