When the Metro is crowded, an item like personal space becomes scarce and finding a place to grab for balance during the ride quickly vanishes. One reason I find myself playing upper-body Twister during crowded rides are Metro Poleblockers (MPs). Not to be confused with its euphenism (Not Safe For Minors), an MP is someone who leans his/her entire body along a Metro pole, thereby blocking anyone from getting a grip for balance. I recognize that leaning on the pole helps you Stanap, and is easier than testing your wrist's tendons when a Metro car is coming to a stop. However, when the train is so crowded you not only find out everyone's perfume, but their favorite toothpaste (if you're that lucky they used some), MPs deny valuable anti-falling over assistance when its most needed.
Whatever it takes to grab space on the Metro.