Just in case you were wondering why Katy Perry and Rihanna are not bff anymore, it is not about Rihanna's drug use. It isn't about Rihanna's boozing or her freaky sexual appetite. Nope. None of those. It turns out that the two are no longer friends because Rihanna is back with Chris Brown and working with him and that is something that caused them to have several arguments and no longer speak. This is not the first time this story has made the rounds, but at least they used to actually speak. Now, it is turning into an active dislike and hate.