From experiences of friends from high school a few years ago turning 'emo'. They pretty much just cried about everything, and had the whole view that life sucked and any little trivial thing in their lives actually made it worse. Not to mention the music they started listening to really irritates me -- it's all about life sucking for such trivial reasons and problems with girls or whatever, and you really need to think if they have even experienced life yet.

I don't generally go by looks to judge if someone is 'emo'. Usually most seem to have dyed their hair black though. Though I'd probably call someone who is a goth an 'emo' because of the way they dress.

Anyways, that's just from my experience, so I'm not going to say every 'emo' out there is like this, just ones that I have met or have been friends with in the past.