Rihanna's Cleavage Challenges Kathy Griffin

4/15/2011 8:00 AM PDT

Rihanna's Cleavage Challenges Kathy Griffin

So there we were ... shooting the s**t with Kathy Griffin in Hollywood last night ... when we turned the corner and walked right into Rihanna. The photog had a decision to make -- who gets the kiss off?!!?!?