A very uncomfortable situation... on the train

I thought getting saline injections in your face looked uncomfortable... wait until you watch this youtube video... (by the way I love the subtitles)

A black girl is on a train yelling at an old woman!! I can only imagine everyone being baffled by this scene unfolding....

I just want to know....

-Who was filming this?
-Who hit the girl (yes the girl gets hit)?
-Why does she start rapping?
and
-What did that poor old lady ever do to her?

Source: Iheartchaos Youtube