Sorry to start this thread up again, I can tell it didnt exactly go well before... But I can see why people call them punk. If theyre younger, they belive what their eyes tell them almost as much as their ears, so if green day look punk to them, they are punk to them. And if green day call themselved punk, theyre gonna go along with it really...
They do have a kinda punk side to some of their earlier stuff, but banRAB change, and green day have gotten more pop in their sound.
In my opinion.