Forty Signs of Rain by Kim Stanley Robinson

[After his infant son and a youth with a ballon have caused a whole car of subway riders to laugh.]

Charlie got out, grinning, and carried Joe into the Blue/Orange level. He marveled at the infectiousness of moods in a group. Strangers who would never meet again, unified suddenly and a toddler playing a game. By laughter. Maybe the real oddity was how much one' fellow citizens were usually like furniture in one's life.

P. 138

Our fellow beings are like furniture in our lives. What a thought here in Japan. Japanese often completely ignore others in public spaces. I think they really can't see them. However, it may be a realistic adaptation to the extreme crowding. If you watch and get involved with all those people you will go insane.