The apartment nearest to mine is inhabited by two people that walk with their eyes cast downward whenever they're in common areas. Attempts to wave or say "Hi!" or engage them are met with a confused upward glance that never actually makes eye contact.
It's probably just me, but my immediate impulse is to assume that I've done something terrible to them in the past while in a state that impairs my ability to recall the experience.
Or you know, they could just be socially maladroit pod people.