When I was a teen, I can never remember being disrespectful towards anyone. Despite that, I was still looked at as a regular snot nosed punk teen, and I absolutely hated that. Yeah, going home after school, watching TV and making sure I was focused on my schoolwork is really being an annoying snot nosed punk teen.
I'm serious when I say this, I never drank, smoked, or did drugs at all. The only bad thing I ever did was skip school, but I'm sure everyone did that.
To answer the question, no, not all teens are stupid. The few that are, though, give the rest a bad name, which is too bad really.