'don't or wouldn't ever know what it's like to be "emo"' - Emo is just a music genre, rooting from Emotional Music.
I wish people would stop labelling themselves, and other people labelling others - it's pathetic! We're all humans and thats all that matters.
But I agree with your point about wearing black make-up etc, anyone can do that, they dont need to fit in with a label or anything.
Plus Green Day isn't even "Emo" music