A teenager is an obnoxious variant of the human species. Teenagers have deep issues of angst and mostly are very egoistic. They tend to be rude to their own parents, but amazingly polite to other teenagers' parents. To punish them God gives them Acne and occasionally makes them pregnant.
Teenagers are rampant on the internet due their parents not being able to deal with them in real life.
Cops may also pretend to be teenagers, as with the folks at pervertedjustice.org, so do ordinary adults. Why they do so, we don't know. Sciforums is not safe for you anymore.