I don't think Chris Brown will be accepting.

 Mixed martial artist Din Thomas knocked his opponent out Saturday night, and offered an encore with another bad ass -- Chris Brown.

...
He told the crowd: "It's not cool to put your hands on a woman. So Rihanna, if you want someone to kick his ass, holler at me."

http://www.tmz.com/2009/03/23/chris-brown-fight-someone-your-own-size/