Mine is the volume of their voice. If all that they can do is just talk too loudly with no reason for it and don’t control the volume of their voice. That to me is a sign that you’re a stupid fuck. Because people think the louder they are, the more righteous and attention seeking they are. Than it is to just listen, digest and respond accordingly to anyone talking around you.
Profession can absolutely affect volume. Even without any hearing damage, any job that regularly requires that you project can become a habit.
I’m a chemistry professor at a community college, fairly well educated, and I flatter myself to say reasonably intelligent, but I still slip into what my wife calls my “teaching voice” in some social settings or even occasionally at home.
Excellent example.