Coca Cola Vanilla Puns

I was upstairs talking to my dad when my little sister came in. My dad had promised that we could have Coke Floats today. (For the uninitiated, a Coke Float is when you get a few scoops of vanilla ice cream, put it in a glass, and pour Coca Cola on it.) So my little sister remembers about the Coke Float thing and starts jumping up and down going, "Coke Floats! Coke Floats! Coke Floats!" My dad just stands there with this really confused look on his face and quietly says, "...I thought Coke sank?"