Not always a reality
The thing about trains is that they get crowded and busy, especially during rush hour times in the mornings and evenings when people are going to and from work. Because of this, personal space isn’t always a reality. If the train had been empty, the youngster’s behavior may have been forgiven and accepted.
Anyone from New York will be familiar with the experience of being forced into a train car like sardines, with no place to breathe, much less move—with an armpit in their face on one side and a guy munching on a tuna sandwich on the other. This youngster didn’t mind taking up too much room.