A co-worker and I were talking about personal space and comfort zones a few weeks ago.  I don't remember why. 

I said, "If the bus is crowded, most often a person won't feel overly uncomfortable if a stranger sits beside them or stands close because they know the other person doesn't have anywhere else to go.  But if the bus isn't anywhere near full and a person takes the seat right beside you instead of in one of the dozens of empty ones, you'll probably feel claustrophobic.  Like they're invading your space."

Her response was, "That would never happen!  No one is going to sit next to someone when there are empty seats available!"

I felt like she was missing the point of my hypothetical scenario, but she also kind of proved my point.  If something like that happened, she wouldn't like it--she couldn't accept that such a situation could occur in real life!

Well, guess what. Today, it happened to me. 

My stop is the first in the route.  I took my seat.  Two stops later, there were six people on the bus.  Then a young man (mid-20s, maybe) stepped on.  He walked down the aisle.  And sat.  Right beside me.

I was perplexed.  There were SO MANY open seats.  Everywhere!  Rows and rows and rows of seats with no one in them.  

I remained outwardly calm while pondering what would make this person select THIS seat instead of any of the others.  Was he planning to get off at a nearby stop and wanted an aisle seat so he could exit with ease?  Does he get car sick in the other (lower) seats and now refuses to sit in them under any circumstances?  Is he perhaps from another culture where this isn't considered odd? Was he, like, attracted to me and wanted to be as close as possible? 

I never did learn the answer to my questions, except that he did not get off at a nearby stop.  I did find that I became more comfortable as the bus continued to fill.  Because, like I'd said back when it was all hypothetical, it doesn't cause as much anxiety when you know the person beside you has nowhere else to go.