Why Did Katy Perry Call Rihanna A Hoodrat?

Katy Perry and Rihanna's very public friendship has been so endearing. After all, the singing sirens seem to have one another's backs: RiRi very much supported her bestie right after her split with husband Russell Brand. So why was the "Part of Me" singer caught calling her supposed BFF a 'hoodrat'? Is their friendship on the rocks?

Nope! Katy was just wishing her newly-turned 24-year-old bestie a very happy birthday, tweeting this:

"@rihanna HAPPY BIRFDAY u hoodrat, bear****, crazy, sexy ass, freaky whole bit beotch. I (heart) u so much. Keep it real tonight, as I know u will!"

So cute! Can't wait to see photos of the happy BFFs celebrating RiRi's birthday! 

Another celeb wishing Rihanna a happy birthday? None other than her unforgiven-by-most ex Chris Brown! He tweeted the following:

Pretty gutsy move for Chris: not only did he acknowledge his ex, but he called her by her real name - a VERY personal touch. 

What's your favorite way to celebrate a birthday?