Keep the Balls Rolling

Listen up, buttercup. This joke is playing on the common phrase "keep the ball rolling," which means to keep things moving or to continue a process. The joke sets up a question about not keeping "balls" rolling, which sounds a lot like talking about testicles. It's funny 'cause it's a sneaky, naughty joke that uses wordplay to make you think of something inappropriate. You probably need me to explain it because you're not smart and easily miss the innuendo.