Our words are more about us than the other person; just because you say to your T, "You're an ignorant, arrogant, so-and-so" does not make her an ignorant, arrogant, so-and-so!
Your T has her own feelings of self worth, her own better knowledge of who she in fact is so your words merely help her see how you view the world rather than tell her anything about herself and hurt her feelings. What you say is not about "her" at all so cannot really hurt her feelings unless she is uncertain of herself and who she is (in which case she probably should not have chosen to work as a therapist).
In therapy, our perceptions of our T are often projections of how we perceived others in our life who seemed to act that way. That's one good reason we don't learn much about our therapist and their lives; to help with getting those projections out in the open where they can be examined by the two of us, together, and misunderstandings cleared up.
When we're growing up we don't really understand the adult world very well and our perceptions of what is going on can reflect that. Unfortunately, when we're 15-20 we haven't have much experience in life either, other than with those close to us and we don't "know" that there's "more" out there.
I vividly remember a hard lesson I had when I was in my mid-20's. My stepmother had been a hard task-mistress all my growing up, was controlling and big on making sure we children did a goodly amount of chores and did them according to how she felt they should be done (can you spell p-e-r-f-e-c-t-i-o-n-i-s-t :-) "Naturally", being a "child"/teen I did not want to do chores, did not understand about pulling my own weight and being trained to be an adult and be able to do for myself "some day" so resented the time I was ordered about. True, her "style" wasn't very kind but my training was pretty good, now that I'm of an age to appreciate it :-)
So, we're visiting a friend of hers, down on the water and having a family day and she and our friend, whom I knew as "Aunt" Martha, were sitting, relaxing with a drink, and my stepmother started issuing clean up chores for me. I'm sweeping and clearing off the table and taking out trash and stacking dishes, etc. and finally I got one "command" too many and rather hatefully spit out, "I hope you're enjoying your bourbon and water!"
My stepmother was never at a loss for words, especially angry or hurt ones. In no uncertain terms she opened my young eyes to all the work she had done to get the party going, versus what little I had done to help with the clean up. Oops. You know how you thought your mother had eyes in the back of her head when you were a child because she could tell when you were misbehaving when you thought you'd hidden it so well? Same thing. I wasn't experienced enough to put the whole picture together and see the entire period of time; how the set-up, cooking, cleaning, planning, etc. were done with me out front riding a bike and playing with the dogs, going for a walk to look for "periwinkles" by the water's edge, etc. while other people were working to allow me that time. It was now my time to contribute to the group good time and I was being a brat about it. Yes, I had a legit complaint about
how my stepmother was ordering me around but. . . it was an ugly comment on my part and only showed me how much I had "missed" about what was really going on around me. I don't make that mistake very often anymore.
Calling other people names, trying to make things about them, almost has to happen until we begin to see and make it all about us. Our lives are about us. How we respond to what comes in, how we deal with what's inside and make sure what we let "out" is what will be most helpful to
us in our dealings with others.
I wouldn't censor what you say to your T, I would try to grab and discuss it, immediately upon saying it if you have a reaction to it. Your T is probably really glad you said what you said because it shows an emotion of some sort. Something "triggered" words that aren't "I don't know" or silence or bland discussion of "isn't it hot?"