Why is it so hardto say what you want?

Been working at McDonalds Skellefteå for about 2 weeks now. And I'm already tired of most people who come to eat. I mean, if they want a cheeseburger, why say that you want a hamburger with cheese on?? or if they want a coke, why say that they want something to drink? And then when I ask them what they want to drink they get pissed of cause they think I should've known that it was a coke even though they didn't say it. Same thing with icecream. They just say that they want an icecream, not which one they want. But what annoys me most is when they want a hotdog... since when does McDonalds have hotdogs?? *sigh*