Not Always Right

Here's what I will never understand: rude customers. Especially the customers who come in and, after I greet them, order their "grande vanilla latte
as fast as you can. I'm running late." And then they proceed to be rude when they don't have it one minute later. Here's my question, well, four questions actually: 1. If you're running late, why did you put yourself on someone else's time? 2. Why do you think it's okay to be angry when someone else's time doesn't match yours? Did you not notice the line in front of you when you walked in? Do you not understand how lines work? The people in front of you get their drinks first. And, though we are working as fast as we can, we are still only human and only have two hands.
I understand that I work in customer service so, therefore, it is my job to serve people. But, personally, I don't think this gives anyone the right to be rude to me or my coworkers. I am not less important than you since I am on the other side of the counter. I didn't make your drink hot when you wanted it iced just to spite you, it was a mistake. This doesn't give you the right to yell at me or treat me like I am stupid. I respect your time, I'm not lollygagging. The real kicker is, if I treated my customers the way most of them treated me then I would get fired. How is that okay? I want to know how "the customer is always right" if the customer is being abusive of the people who are serving them?