same here; I keep reading that every T is well trained to weather storms from clients, on the contrary really wants to see you reacting in the moment, but in fact every time I went ballistic in her office, I could see in her face that she was not taking it calmly. It seemed to damp her confidence more & more, and in the end she said she couldn't help me any more.

I'm not sure that the paper "tantrum" is any better, if it's given to T where he/she can read & re-read it;
maybe better to go in with it,
preface it with 98574637485 apologies & caveats,
read it out just once,
and then chew it up and swallow it.

sound like a plan?