I'm fed up of hearing the phrase "just a teenager." I don't think people realize how offensive this term can be. When talking about different things we are often told that we won't understand because we are "just teenagers."
However, I think the worst case of this can be when we teenagers go to adults with our problems. Now, obviously adults have their own issues like mortgages; credit cards; putting food on their children's plates etc, but that doesn't mean that they can't put in time to listen to our problems. Or if they ask about how our days were, at least look like they care or have an interest in what we are talking about.
There have actually been studies on this kind of thing which say that if a 6-year-old comes to you with a problem and you dismiss it, they are less likely to come to you with issues as they get older because you'll have ignored their problems first of all. However, if you listen, they'll come to you again in the future.
This is why teenagers tend to talk to other teens about their problems, or just keep them to themselves, because it's easier than being laughed at.