Juxtaposition

Earlier today, I stopped in the neighborhood market to grab a couple of things suitable for my day of lounging. I couldn't help but shake my head as I paid for the stuff: a 2-liter of Diet Coke and a pint of Ben & Jerry's Vanilla Heath Bar Crunch. What's that about? And if I finish both of them by the end of the day, do they cancel each other out? Or I will I just be a tad fatter and unable to sleep? These are the questions that consume me.