I'm too much of a pussy to ride the bus here in Atl but in Spain it was about 50/50 that there would be a drunk person singing on the bus. The train was a little more unusual, like the gothish guy who sat with his head on his knees drooling on the floor for 6 stations only to stand up and give everyone a hate filled glare before stepping off.
This is what I miss about Seattle karaoke, when people didn't give a shit about anything other than having fun. (San Francisco karaoke is SRS BUSINESS.)