I have a problem with graffiti if it's:
1) Vulgar or obscene
2) Gang related or promoting violence
3) Obscuring the useful information already present (like on a highway or street sign)
Granted, that covers a LOT of graffiti (that I've seen, at least) but if it's done to actually be art, I don't personally mind. I understand that graffiti artists are vandalizing property, but if it were my building I wouldn't bother spending the time and effort to remove PG graffiti, thus negating one of the complaints regarding it.
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack