It's when you're on a bus that takes a slightly different route because of roadworks or some other obstacle. The collective horror and bewilderment among passengers as the bus makes that surprise turn down the unknown road of mystery & horror...
 
"What the.....where.....who....why? What's going on? THIS ISN'T NORMAL"...and passengers who had previously been doing everything possible to avoid each other's eye are suddenly brought together in this shared experience of intense befuddlement and terror. If there's one thing that gets strangers talking to each other on the bus, it's a minor diversion from the posted route. These small things amuse me....

Good observation. It's funny how a bunch of people can suddenly snap out of their semi conscious states when there's a disruption to the routine. As you say, when you expect to go left and you go right instead, alarm bells start ringing.

I noticed a similar reaction the last time I boarded a bus holding a running chainsaw... 
 
(Ok, ok...  I honestly can't remember the last time I was on a public transit bus!  Probably 35+ years ago?)

Oh you would love NYC buses at rush hour. They're full of coarse mannered idiots bickering over seats and "tough" guys with fragile egos who can't handle being jostled. Yesterday it was standing room only and this large dude was stood right next to one of the back doors playing Candy Crush on his iPad. The long handles on the doors are touch sensitive and open them at stops. At every stop, after the doors had closed, he would lean against the handles and the doors would open on him, causing him to yell "who's doing that? I swear to God...is that the **** driver? What an ****!" It happened at every stop and each time he got angrier. Nobody had the heart to tell him he was an idiot. I was sorely tempted.

Hi,
 
Oh my ... Magical Mystery Tour?