I don't think a therapist should try to get you angry at them by doing mean things. For one thing, it is dishonest. They are saying the mean things just to get a rise out of you rather than because they necessarily believe them. I think this approach could lead to a lot of distrust between the client and therapist. Plus, it seems like there are often reasons for a client to be mad at a T lol without them having to deliberately be mean. I think also that the therapist could try to get you to express your anger at other people in your life that you are angry at during your session. For example, if you are mad at your supervisor, the therapist could try to get you to express that to him. Have you tried that?

I too have trouble expressing anger; I don't even get angry that much since I probably submerge it almost instantaneously. There were a couple of times that I got angry at my T, though, but not because he was deliberately mean. Believe it or not, it was really helpful to get angry him! He didn't get defensive at all. He thought it was great. From this I learned I can get angry at a person and survive the experience. A couple of other times I was able to express anger about other people during my session.

For me, the first step in this was learning to know when I was angry. It sounds like you are already able to do that, which is great. How about trying to express anger over your supervisor the next time you have therapy? That would be great practice, and much better than practicing on your supervisor him/herself.