• When they figure out something about you, that you don't know about yourself.
• When they can get attention off people, and make it look unintentional.
• When they are charming or manipulative, to know how you're going to react to something before they do it.
• When they say the right words at the right time, so you are drawn to them hoping that they'll trigger an emotive response with you again.

You know when you're around someone who is emotionally intelligent, because you don't have to tell them how you feel. Either because they already know, or because they make you feel special so you don't have to.