It's been reported that Rihanna's friends have started to grow increasingly concerned about the singer's blossoming friendship with Chris Brown. We're sure you don't need reminding that Chris and Rihanna used to be an item until that fateful night when he beat the living daylights out of her. No, we thought you were probably up to date with that one. So anyway, a source close to the former couple old TMZ, "Rihanna and Chris are dangerously ...