"Self important bitch"?
That's a bit strong mrspirite!
As far as being 'self-important' - she's a pop star, that's part of her job description!
Re. the 'bitch' part - without serious evidence, this just reads as a nasty insult, so i will ignore it.
Rihanna may have had a valid reason, beyond her control, for the delay in her arrival - it happens to musicians as much as anyone ele, it's just that the media makes a meal of it.
As far as walking out - that means that audience cuts off its nose to spite its face, and audiences are not known for such behaviour.
All cleared up now? Good.
Feel free to ignore pop stars if they irritate you so much.