I don't like it when teenagers roll their eyes at me. Of course, I remember doing just that to adults when I was a teenager. Sometimes I feel like I've won the argument if I get the eye-roll. Other times, it just bugs me. I think the eye-roll would certainly be a demonstration of disagreement coupled with disrespect. But it also shows that the teen doesn't knows that they shouldn't continue with the argument and it is like their last display of rejection and rebellion. In order to improve the situation, I should realize that if a teen gives me the eye-roll then maybe I've presented my message a little bit too strongly than I intended and I should modify my body language and voice to make them not feel attacked.
Given that this post has been made before, and I replied to the first question, this response will address the fourth question.
Typically, people do not know that their behavior makes another unhappy (if nonverbal cues are not given--which would show the unhappiness). Unless a person is upfront and tells another person that their nonverbal cues are hurtful or unaccepted, the behavior will not change. Behaviors can only changes if a person is made aware of what they are doing. That being said, some nonverbal communications are very hard to change--many are involuntary reactions (given they have been "used" so much)--just ask my teenage daughter.