And now the Municipal Transportation Agency is looking into the incident, which occured on the 20-Columbus line.
A passenger eventually broke it up, though at least one egged the pair on in Cantonese, according to a translation.
Drivers are supposed to report incidents like this at the end of their shift, but frankly, it's a pretty typical scene for anyone familiar with the neighborhood.
Buses running through Chinatown and North Beach are often jam-packed, and run incredibly slowly, leaving riders frustrated and likely late to their destinations.
Still, if you think that's ugly, just sit back and watch the long-running fights over the Central Subway boondoggle.
Hell hath no wrath like a Telegraph Hill dweller or Chinatown powerbroker scorned.
Jackson West is more surprised that anyone was actually able to find a 20-Columbus.