Harcore is not about fashion. Harcore is not about who can be the most "scene". Hardcore is about the music. I'm not sure where the confusion in what hardcore is started, but it has always been about the music. Here's a little history on the music.
Hardcore stems from the early punk movements in the mid-70s made notable by bands like The Ramones, The Clash, The Damned, and the Sex Pistols. Most of the fast paced, straight-forward sound that is hardcore can be heard in early punk. As more and more styles of the punk sound formed each year moving towards the mid-to late 70s. A newer sound of bands like The Misfits, The Exploited, GBH, and Black Flag would lead the move away from the sounds of this early punk.
This new style involved a faster, more technical drum beat and simplistic bass lines. Moving into the 80's the term hardcore is often credited by the band D.O.A. due to the title of their album Hardcore '81. As was seen in the origninal punk movement, this new sub-genre had the same do it yourself attitude. This attitude is the resounding theme of all hardcore music. The overall image of harcore was different, bringing the simplistic look of t-shirts and jeans to the table.
Founders of the Early Hardcore sounds can be heard played by the bands Black Flag, Bad Brains, Minor threat, The Mob, D.O.A., Middle Class, and Dead Kennedy's.
This new style of music became associated with violence due to the inlaid aggresive element to the sound. This aggression laid the ground works for slam dancing and stage diving found at most shows during these times due to the relatively small venues and easy access to the stage, which was not usually seen in most mainstream rock shows.
This early harcore sound had a major influence on forming genres of music such as, Thrash and speed metal, and later on the seattle grunge sound of the late 80s.
Moving towards the 90s hardcore began to branch off into many styles and sub-genres. The hardcore sound had two main branches the punk based sound of the 80s and a newer metal influenced sound, which later is the basis of most of todays metalcore bands such as Unearth, or It Dies Today. The late 80s and early 90s punk based harcore sound can be heard influenced by Agnostic Front, Sick of It All, Cro-Mags, Murphys Law, and Gorilla Biscuits. The metal influenced version of hardcore can be heard in the musical stylings of the bands Madball, Biohazard, and a more recent example Hatebreed.
I have used many of the obvious examples of what the hardcore sound is and was. There are many bands today that still have the traditionaly hardcore sound. Most of what todays youth actually call hardcore is a more diverse metal influenced subgenre of the original sound. It is imprortant to understand the roots of something that seems to be exploited to todays teenagers.
More recent hardcore of the late 90s and today. Examples include some of my favorites:
Comback Kid, Blood for Blood, Blacklisted, Integrity(formed in the 80s and still putting out records), Lifetime, and Rise Against. There are 1000s that I can rattle off.