[lvs]

That's a bit stuffy. I'd be honored to have Banksy paint my stuff without permission.

[zombio]

By saying that you are giving him permission.

[cjg]

But even if he hadn't said it, it would still have been true.

[Millennium]

I'd probably say yes myself, but I would really, really rather be asked first. That's just basic respect for one's fellow human beings.