Graffiti can be both art and vandalism, it's vandalism if its prohibited in the area, if the owner doesn't want it, or if the owner doesn't know your doing it. It's an art otherwise, I call the legal graffiti "The Urban Masterpieces"
I don't consider meaningless gang signs, racial slurs / hate speech or vandalism on memorials/monuments/headstones art. I consider THAT graffiti.
But this "graffiti" that is considered "art" by many / what comes to most peoples minds when they think "art that isn't graffiti" isn't "graffiti" in my terms, really, it's "street art" or a "mural" for example. So, with this kind of thing, if it's considered and called "graffiti" by the majorityit isvandalism, if it is considered street art or a mural etc, it is art. You wouldn't call that graffiti, would you?
This being said, and I think I'm making a big point here, political or activist graffiti (that is NOT hate speech, bigotry or bullying) has been used as a tool to get a message across to the masses even just a small community... IS ART, and has and can be seen as very rude / unsightly / distasteful to others, yet it is very effective and can send a huge political/social/emotional message. This is one of the biggest examples of TRUE art in my opinion. Not ALL art is loved. But strong criticism from both sides is what defines true art. Art is one of the most useful tools we as humans have.