It Isn't Too Difficult

I've mentioned before that I don't drink soda. It's really the only healthy thing that I do for myself. It takes dedication sometimes. It isn't that I miss it, it's just trying to find a replacement for it can become more of a hassle then it's worth sometimes.
When I eat fast food, I order milk with my meal, instead of soda. What really sucks is that not all fast food places even carry milk. We live in such a healthy society. About 75% of the time that I order a milk, I'm told by the cashier that they aren't able to do that. I always let them know that, indeed, you are. They claim they have to give soda with a meal to which I respond, "Can I speak with a manager?"
Sometimes, I just get really odd looks from the workers, as if they can't believe someone would drink milk instead of soda. Get over it, it's what I do. The rest of the time, they just completely ignore me and hand me a cup to fill with soda myself, as if I may not notice.
Today, I had the unfortunate problem of having to eat Burger King for dinner. I actually like Burger King's food, but they always screw up my orders and take forever. Anyhow, I ordered a milk and paid with my debit card because I never carry cash. Psycho, I know. The girl handed me a cup for my soda, and I said, very politely, I actually wanted milk instead of soda. She was really embarrassed and then told me she needed my card back so she could run a void on it, since a meal with milk is cheaper then one with soda.
I'm sorry, but if you can't follow a simple request when I order food, I'm not giving you my card back so you can try to run a void on it and then run another transaction. I'd probably end up with a couple hundred dollar transaction on my next statement. I told her not to worry about it, and she gave me my milk.
I know I'm a picky eater, but is my request really that unreasonable when I get a milk? I just don't understand why no one is ever able to get it right. I should file a lawsuit against fast food chains saying they're trying to force me to drink soda and there by making my teeth rot.