"Let me guess, a costume is anything you personally don't wear?"
Guess again.
"Newflash pal, there is a practical purpose behind almost every article of clothing that I wear."
Never having seen what you wear, I will not comment on that specifically. I will, however, make the general comment that there is practical, utilitarian motorcycling apparel and equipment that does not add up to an "outlaw biker" costume.
"If you want to talk about costuming, let's examine the necktie which serves no function whatsoever."
Okay. That is a costume that says, "I do feel morally constrained by society's customs and laws. I will not stomp you, shoot you, or rape your daughter. I accept my responsibilities as a member of society, and most likely have a productive job. Further, I have enough respect for you to communicate all that by wearing this costume."
As for this whole costuming thing, no, I don't dress to inform anyone that I'm going to rape their daughter. I dress the way I dress because well, I like it. I like the tattoos (and God knows being Japanacised you'll have opinios about tattoos)I have and may get more. I like the steel hoops in my ears. I like my beard. More importantly, my wife likes the way I look and that leads to much snoo-snoo.