Me: I call my girl Cinderella.
Friend: Why?
Me: Because she loves balls.
Me: I call my girl Cinderella.
Friend: Why?
Me: Because she loves balls.
Listen up, buttercup. This joke is all about that "double-entendre" thing. Cinderella is known for going to fancy "balls", but the dude is also implying his girl likes... well, you know, "balls". Bet you didn't even notice that, did you?