at a place that has a mailbot.
Or a mailmobile, rather.
I was walking out of the lunchroom, and thought someone was pushing a huge mail cart in front of me, only to have the thing beep and shuffle and continue on its merry way sans operator.
It might as well have had a toilet plunger aimed at me and "WE ARE THE SUPERIOR BEINGS! EXTERMINATE!" issuing from its buzzing corpus, for the look of Shock on my face.