Not exactly went off on a customer.

I work in a Tier-3 technical support job, and this happened 1 year back when I was new at my job. We had this one particular manager at work who kept insisting on being a dick to everyone. We being newcomers didn't know how to react in such a scenario. The man was just trying to establish his sense of authority and dominance, which seemed really petty to me.

One fine day, One of my seniors at work decided to stand up to him , and confronted him about the shit ass way he treated the employees.

His response was by humiliating him at every chance possible. I have never seen anyone hold a grudge as strong as that man. He went about causing him discomfort at every possible scenario. Emailing him with some higher ups in CC, questioning his work quality in front of everyone, etc. His main aim was to cause him stress and discomfort.

He succeeded it as well. My senior got so pissed off that he had to switch jobs.

That manager has moved to a different team since then, but that man is still hated the most in our work group.