Both. Graffiti, and I mean true Graffiti is an art expression, that takes much of dedication to deliver right. That human face in the top picture of the meme, may have odd colors, but the shapes are anatomically correct, which does require skills as an artist. The bottom one is also in a certain way an art form. It's not even usual that graffiti is, like any other form of art, used to make a statement. For example when the Berlin wall was still up during the cold war, many tourists came to West-Berlin to see that wall, much to the displeasure of the locals who hated that thing. Somewhere somebody wrote in graffiti style letters "Nie eine Mauer gesehen?" on the wall which translates to "Never seen a wall before?" I think the message was clear....
The downside of graffiti is of course, that quite often they are placed illegally on objects never meant for this purpose, and that's where it becomes vandalism. Some places being painted are even private property and when painted on without permission of the owner, then we do have a problem. When it comes to public property it's not that much better, as our tax money is then used to remove it, and I'd rather see it spent on something else.
Now I do know a Dutch graffiti phenomenon called "De Kabouter" was quite a hit, and I know somebody (who didn't know who the "artist" was), placed a slab with a note requesting to draw "De Kabouter" onto it with a can of beer as a reward. The next day, "De Kabouter" was indeed painted onto it and the can of beer was gone. Can't speak of vandalism in that case, can we? I've also seen a few tunnels for pedestrians only that were entirely painted in graffiti by artists hired by the local authorities to do so. This is also due to a kind of rule that you don't put your graffiti over somebody else's, as that means disrespect for a fellow graffiti artist. Although there are a lot of people ignoring that rule.
So yeah, graffiti can be art, in different styles even, sometimes conveying a message, sometimes just set up to be beautiful, like any other form of art. It's just that it's placed unasked and unwarranted on other people's property that makes it vandalism.
