I've had a couple of situations that may fall under this category, but only with someone who seemed SERIOUSLY unhinged, i.e. (both times) the person was yelling and screaming. Actually, this happened to me with a doctor once! His receptionist called me back to quietly apologize. I think he may have had dementia or something else (I mean I'm no diagnostician, just guessing) and that the office had experienced this screamed-at-and-accused-by-a-doctor (at the end he was shrieking himself hoarse accusing me of attempting to refill the Ritalin prescription that he himself had been prescribing for my stepson for a year because I "just wanted to take the drugs [myself]" and I "just wanted to get high") before, with other patients/parents of patients. So it was pretty clear I wasn't the crazy one. Well, that time at least. (Kidding...sort of...)
But it isn't like this is a regular thing or anything. I think I would just feel sorry for the person. I certainly felt sorry for that doctor. He was off the hook, I thought he was going to have a heart attack. And who knows what on earth he was going through or what issue or illness he may have had. I think I was just glad and grateful not to be in his shoes.
People go through all kinds of stuff and people do get ill, I really try not to judge; I don't want people to judge me so I feel that's only fair. But if I felt in immediate danger in the situation I would most likely back off quietly and just let the person feel s/he had had his/her say, whatever it was. In the case of the doctor, I just quietly hung up the phone. I have no clue what he was going through. I did ultimately get the refill my stepson needed and we switched doctors so there was no real permanent harm done.