Oct 7, 2009 10am, Chinatown San Francisco. This fight occurred on the Muni Stockton route (the 9 i think) just before the stockton tunnel. As you can see, a simple argument about seat-hogging quickly turned into a full blown brawl. It's pretty clear who threw the first punch, you can see the bus' serial number, and the exact time in the video.
But the version with Chinese subtitles is so much more illuminating!