Let's say the train is super delayed.
And after waiting for a tain for thirty minutes one blows by half full.
And then ten minutes later another one blows by, not even slowing down, and is again half full.
And then, another five minutes later, finally a train slowly draws next to your platform. And it's packed.
Everyone is in a bad mood, but everyone knows everyone else is suffering through the same hell so there is a certain amount of civility, even though we're all packed in and closer to each other than most couples are even in their most intimate moments.
And then, three stops later, two people leave their seat and the person next to that seat does this: