IMHO this is about metal heads knowing that each of them is a bit silly, different and strange in their own way. But still able to hang out and have fun doing that. Also I would say that metalheads are generally less aggressive that other people. It may be connected that you are able to just channel that aggression in headbanging during concert :) If we are talking about concerts: knowing the fact that you are not exactly 100% normal and still be able to sign the lyrics with hundreds of other people, this feeling of unity, awareness that you are not alone, it is great. Especially in the current world when useless internet points, in a manner of likes, are to many humans source of feeling about themself. We are after all social creatures. Being accepted is very important to us.