It's not quite graffiti but I still think <a href="http://en.wikipedia.org/wiki/2007_Boston_bomb_scare">this</a> is along the same thing. Although to be honest I just love it because of the <a href="http://www.youtube.com/watch?v=4XTuiyJNJOI&fmt=18">interview</a>. Best street theater evar.
If we're just talking about graffiti though <a href="http://www.banksy.co.uk/outdoors/horizontal_1.htm">Banksy</a> is one of the most amusing guys out there. <a href="http://www.banksy.co.uk/outdoors/images/landscapes/piltonfrisk.jpg">This one</a> particularly amuses me.

