When used as an adjective, emo generally refers to an individual who is either over-emotional or tends to exaggerate situations. For example, you may call someone emo for crying over something that really doesn't merit crying. However, it is good to use the word withcaution because it generally carries a negative connotation.
Girl: Nobody loves me, my friends aren't really my friends, nobody cares about me, I'm all alone, I'm always so caring of other people and no one cares about me, I'm so selfless!!!!....etc.
Me:.....GOD DAMN, YOU ARE EMO!