I've gotten into this discussion far too many times than is probably healthy (I should train myself to just walk away when I see the words "punk" and "dead" in the same sentence together, as it is never a good sign), but I am genuinely interested in the opinions of people here.
It has become accepted by kids my age that the only way to be punk is to never, ever say call yourself punk, and to vehemently deny that you are if someone else does. Saying that you're punk is automatic evidence that you're a poseur.
I, personally, think this philosophy is bull. If you love punk music, go to punk shows, enjoy the punk "lifestyle", what's wrong with calling yourself a punk? Why avoid saying that you're punk, if that's what you're into? Because you're afraid other people will call you the (other) p-word?
People also run around saying that punk is dead, without any real reason. Sure, people have capitalized on the whole rebellious appeal of it, and there are always your Avril Lavignes and your Ashlee Simpsons, but there's still a thriving scene and, in my opinion, the punk spirit is something that will never completely disappear.