Public Transport Etiquette
Rule 1: give people more room if the bus is empty

When the bus empties and you are the only two left on the bus, strangers sharing a seat, there is an opportunity that opens up when the outer person can choose to move. It shuts after about five minutes where upon they feel they must stay put so as not to offend you by making you feel there is something wrong with you (like you just farted or something) causing them to make the move. So they don't move and you both sit there on an empty bus right next to each other crushed onto the seat. You, as the inside person, are left trying to will them into moving while feeling more and more claustrophobic as time goes on.

So when the bus empties and you're the outside person just MOVE.