Hmm. I would have to say Right Brain Introvert, simply because they can be so hard to read and so easy to blow up. One of the mares at my barn seems like a RBI to me, but she has a really short fuse. I've ridden her once, and she leaks tension. Every single step, twitch, and movement was short and quick, with no softness whatsoever. She just gets so frazzled and frantic. She doesn't go into the wild panic mode right away, but can if pushed.
She's also in her late teens. So she's lived this way all her life. Poor thing.