Apparently because of this: "You are absolutely not entitled to not do your job, unless you're not getting paid for it. Every job, every single fucking job, you ever have there will be bad people to deal with. That is not an excuse to be a fuck up.
Also, I'm generally a pretty good customer to deal with, but whether I get the product I paid for being based on your mood and how catty you're feeling that day is not appropriate. It doesn't matter if "I'm not the type of customer you're talking about". People pay for coffee. People receive coffee. That is not optional.
If you're that upset, use the "right to refuse service". Except, I'm guessing that you not serving people their coffee would piss off your boss, wouldn't it?

Also I'm a criminal and a cunt.