"Emo" used to be used to describe a genre of music, "emotive" something or other, and now it's expanded to mean people (usually teenagers) who are always sad and/or looking for something to be sad about. Like lovely posts on noticeboard asking for the blooper reel, la la la...

If you look around LJ, there are a lot of icons with the caption, "Cheer up, emo kid!" Never fails to make me laugh. *g*