As a slightly younger teen (17), I have a completely different view of Twitter. I'm not sure if it's unique to my specific area, but quite a significant number of the people around me are on Twitter and use it to communicate funny things they see, or just share opinions (I guess the author approaches this with "complain/express yourself"). To me, I go on twitter to see what people are saying about any given event, especially sporting events. At other times, I will find memes or jokes or just anything that is somewhat funny. Overall, the three groups that Andrew brings up aren't really complete.