Whether you try to or not, everyone expresses something about themselves through their clothing.
Some people dress in a certain way that screams "I'm different" with any number of other perceptions possible. Why they see it necessary to stand out, I don't know, but I wouldn't guilt anybody for stereotyping them and feeling uncomfortable around them.
The average person is law-abiding and has agreed to abide by their society's collective values. By demonstrating that you're different by your clothing, demeanor, personality, or whatever, all that you tell people about yourself is that you're "different". All that people have to go by is their personal experiences, stereotypes, fears, etc.
So what's the point? If you demonstrate that you're "different", you'll probably be treated as such, and that's the reason a lot of people dress uniquely in the first place in my opinion; for attention.
Considering that "normal people" abide by the law and agree to society's conventions, trying to garner attention by dressing in a way that says "I'm different, and I have a gun" is certainly a legitimate cause for attention. The thing is, it usually makes me give those people the "bad kind" of attention, and obnoxiously, I think that's probably what they want; for people to fear them for some reason; to be seen as "tough".