Lift heavy; do Jiu Jitsu - deter the manager from ever attempting to verbally abuse you lest risking discordance. Relish in your newfound mental clarity.
But I would not handle all such social situations so quickly or confidently. And sometimes the moments I miss are opportunities to be nice. The point being that moving along a personality dimension can't replace a missing skill, though it can partially amelirate the effects.
The problem is getting past freezing up. It's hard because it was my brain's innate reaction all through my young adult years, so I had to put a lot of time and energy into rewiring it to not freeze up first.
Once I could get past freezing up, I could practice ways to stay rational in emotionally charged situations, which in turn allowed me to learn how to defuse situations better. With more practice, I was able to manage the same situations with a strong sense of principle. That in turn let me say "no" in a way where people consistently respected my answer.
But that was a 5 year journey filled with unpleasant moments.