On-site advertising/guerrilla marketing stunts are becoming a more and more popular medium, especially because of the possibility of creating low budget solutions that later have a great impact. Usually, the greatest stunts were the simplest ones, yet when caught on camera and uploaded online, the videos became viral almost instantly.
A great example of a stunt that conveys a clear message in the simplest possible way, thus having a big potential to become viral is the new one from Ogilvy Brazil, created for Allianz insurance company. The stunt was performed in a bar somewhere in São Paulo, and the idea was to raise awareness of the dangers of drunk driving. Not to be too revealing, I advise you to take a look at the video yourself: