When and where did it all start?
New York, 1960s. Political activists started using graffiti as a form of expression and street gangs like the Savage Nomads use it to mark their territories.
By the 1970s people started to realize graffiti as an expressive art, an individualistic style, and it started to become competitive. In 1980, graffiti was associated with emerging urban cultures like breakdance and rap music - as produced by the 'neglected' youths of New York. These took form in performances, shows, and movies.
But don't let this confuse you since it was documented that the graffiti artists of the seventies listened to rock and Latin jazz, based on studies by a cultural critic named Goldstein. When you think about it, the solid association between hip hop and graffiti was because of mainstream media.
Since the inception of the link between graffiti and hip hop in New York, the fashion statement of graffiti artists also evolved. You can never know if the person sitting beside you is a graffiti artist. There are those who love wearing artistic and psychedelic shirts like this, and this. Others wear graphic hoodies paired up with uniquely designed socks. While some artists just wear plain outfits and blend with the crowd. Why do artists want to 'blend in the crowd' you might ask?
There's this debate about whether graffiti is considered a form of art or vandalism. You can search Google for the history of it and find lots of articles about it. But in my opinion, if you own a property, with huge empty wall space, and you give consent to a graffiti artist to perform his or her magic on it, it won't be considered vandalism, but a form of art, a mural even. But if artists do their magic without the permission of property owners and go running in the night, then it's vandalism.