Sounds like you want to change this pattern and that is admirable and should be something that moves you forward in your relationships with everyone. I could be a smart @ss and say just change it, or continue to change it because you already have.

In my version of what I think your "tell T x or y or z" is, identifying what it is I needed to say was about 2/3 of being able to say it. It's a big step. Then for me the next was feeling willing to say x or y or z. It was important for me to be able to do this outside the T room, so it was a good chance to practice. I'm guessing that there are other people in your life that you might want to say you are or were mad at, or wanted to tell them they were mean. Or at least contemplate the possibility rather than pretending it doesn't matter.

I'm sure you know the general basics of communication that deals with your feelings towards another person. Perhaps one of the least confrontative ways I have done this with my T is the "I feel/felt upset and angry when you said this thing, and I'm curious about why that is." Use "I" statements and be specific, so "you are always mean to me" is likely to lead to a productive conversation, but "I was angry when you said this specific thing" is not. I like to use the curious tag because it takes the issue out of the realm of finger-pointing or telling her she's wrong and focusing on my reaction.

And then when I learned to do this in the moment, that was pretty cool. I realized i could say what I felt without the world dropping me into a sinkhole, and I became better at it with people in my life.