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.
I drove a base model Ford Fiesta about five years ago that did not ship with cruise control functionality of any kind. I was surprised as well, but the practice does exist.