Take it as a learning opportunity in general customer interaction. You're working with a shorter fuse than normal with alcohol dulling inhibition, but usually being open as to why you cannot do something, before assumptions kick in, is helpful. "No, sorry, she's refused it. I cannot. It's the law." "No, sorry, I can't serve intoxicated people." In every customer service training I've ever received, it's been drilled in over and over that you cannot assume a customer's experiences. You cannot know if they were snobbed in favor of white folk in a store that afternoon, or if they were laughed at for applying for a loan last week. There's only so many times you can get hit by something before you react reflexively when someone makes similar motions.