Graffiti is defined by it's vandalism. This is not to say the use of spray paint or urban art style indicated that the art is vandalism, but graffiti is marking up something that doesn't belong to you. I don't give a damn if it's da Vinci drawing an original masterpiece, if it is done on something that doesn't belong to him without permission, that's vandalism.

I dont think graffiti artists would appreciate if cubists or surrealists started vandalizing their property with their own definition of good art, so i don't know why the vandals feel their art deserves respect. By all means, tag shit up, make murals, draw big fancy tribal words, but don't do it on other peoples property. Buy a canvas and be an artist, not a vandal.

And having said all of this, a lot of graffiti, all of the graffiti i can see from my window, for example, lacks artistic merit as it is just a bunch of hastily scrawled acronyms and gang signs. This describes much of the graffiti in the world, and there is nothing good or artistic about it. I equate this more to a dog peeing on a tree and thinking that it makes the tree his.

Graffiti is a form of art, that can look really cool but it is also vandalism. Vandalism simply means "Willful or malicious destruction of public or private property" you can be as artistic as you want but it would still be vandalism. So i would call it both.