50 Cent's done with Kanye West. His next competitor? Lance Bass!

Both Fitty and Lance released books on Tuesday (50 x 50 and Out Of Sync, respectively). "He doesn't stand a chance," Fitty told the New York Daily News. "With me, everything's a competition, so I bet you the end of next week, I'll be moving more copies than him."

But Lance is ready to bring it. "50's going down, that's all I have to say," Lance replied. "50, I don't want to playa-hate, but there's a lot that my book has [that his doesn't]…I'm pretty sure he doesn't have any relationships with guys in that book. And I'm pretty sure he doesn't have any space training, either."

Oh snap! We're sure Fitty shaking in his boots.