I see the "not brutal enough" discussion only in the internet, because that's where the morons dwell. When I meet metalheads in person, they are mostly pleasant people who are knowledgeable and mostly open minded about music, although most prefer to be at least a bit "UG" when it comes to music in general.
I really think that most of the most loud "act stupid and be elitist" crowd in the internet is under 17 and going through puberty. I was very much like that when I was sixteen, but I've grown since. And please people, don't take this as "everyone under 17 is an elitist" or some other generalization like that.
I've never encountered the "metalhead are stupid" stereotype someone mentioned (and I've seen it mentioned a lot elsewhere). But on the other hand I have lots of experience with "metal is immature" attitude, which is pretty near, and can drive you nuts too.
And about appearance... I have long hair, because I like to headbang on gigs and it's more fun with hair. It is rather unpractical though and I've been thinking about cutting it short. I wear mostly black, but some other colors too. I was very much into the "metalhead look" when I was younger, and the black just stuck. It's simple and I don't have to wonder what colour goes with what.
I do have three band shirts, because I like to support bands and also show the support. Someone might even find a good band because they see a logo in a shirt. I do have some sense of aesthetics though and I only buy a shirt if it's not too "loud". Simple logo and maybe something small on the back, preferably in just black & white. No CoF shirts for me thank you. This is also the reason I only have three of them, hehe.
That said I, like others in this thread, also enjoy other music besides metal. Only things I have real problems in music are rappers who don't rap "to the beat" and trumpets in jazz... they just make me cringe. Although I think it's just a matter of getting used to. Music is like beer. I didn't like Guinness Special Export Stout at first either, and now I just get euphoric when I drink it.