When you purchase food in a restaurant, it is generally considered polite to thank the person who serves it to you.
Some people believe that this sort of common courtesy does not apply in the fast-food environment - fair enough.
So if you are one of those who believes that plunking down $4.39 for the jumbo-sized extra value meal entitles you to take some stupid teenager to task for his fashion faux-pas, by all means go for it!
IMHO, you're wasting your breath - after all, this is just some stupid teenager making minimum wage, if he actually took pride in the food or the service he'd be working at a real restaurant instead.