What does this mean (English)?

[Celeste]

Justin Bieber wrote on twitter "hoping we can continue to change the world together." and then this girl hash-tagged him and said "how exactly are you changing the world, you pretentious little sh*t"?

I dont speak english very well, can you please tell me what did she mean by saying this? Thank you.

[Aaron]

She's clearly being sarcastic or insulting and certainly doesn't believe Bieber is changing the world. Pretentious means to pretend to be greater than you are to impress somebody. The sh*t bit was an insult.

[Dale]

She was trying to say that Justin Bieber is not doing anything useful to help the world. She was just proving her point that JB has done nothing to change the world by questioning him.
She is a smart girl...