When we got to the BART station, he was one of the first people up, and he continued to chatter away as he left the bus. As he left, nearly the entire back of the bus, including I must confess me, cracked up over this poor oblivious fellow. One man on the bus shrugged and said, "So much for the floor show."
I might add that I'm afraid that this guy had what I thought was a "fannish" look about him. Not that every person with social obliviousness is a fan, but it seems to track high with people I think of as fannish. Including, from time to time, me.