That cracks me up too, all that fat in fast food turns to sugar too. Here's my order 2 burritos, 2 tacos, a quesadilla and oh a large diet coke. I'm so used to it now I couldn't do regular soda.
That's how my dad is. He's diabetic and has been drinking diet soda for over 10 years. If he even smells regular soda, he wigs out. That's about the only part of his diet that he actually sticks to.
When I was a pizza delivery driver, we'd get some weird orders. One of the weirdest I had was a Vegetarian Pizza with Beef and Pineapples. We all were like, wtf?