"Throw your money in the air
watch everything fall apart
have some more, have some more
That's how we do it
I spend lots of money
But I still have plenty
I can drink as much expensive alcohol as I want
And I still have money
Up all hours of the night spending money
and I still have plenty
That would be the first few lines break down."z

Basically this song is talking about someone who is so filthy rich that she can do whatever she wants, whenever she wants and never feel the dent in her pocket book.
This actually makes sense because Rihanna's net worth is 120 million dollars.
And while she isn't always in the spotlight like Lindsey Lohan and Paris Hilton have been off and on for being party girls and living exactly like the song describes, if Rihanna so chose to be she could and she would never notice money missing from her extensive amount of assets.

http://www.dailymail.co.uk/tvshowbiz/article-2684901/Rihanna-worth-120-MILLION-carries-expensive-Louis-Vuitton-purse-lands-New-York.html