This happened to me a few years ago and it also happened to my co-worker recently, so I'm going to share it.

We sell food where I work including pizza. A customer ordered a cheese slice. For some reason, stupid me thought she meant an actual slice of cheese like Kraft Singles. I had such a puzzled look on my face when she ordered it. I said to my co-worker "Do we have any cheese slices?" and he brought me over a slice of cheese pizza. I finally understood. For some reason, things didn't register properly in my brain.

The same thing happened to a co-worker last week. I wasn't working in that stand, but somebody told me about it. In this case, she actually brought the cheese slices (which we have for burgers) out and the customer saw and was laughing!!!

Ha ha. When I was very young I was waitressing in a tourist town called Queenstown. An American asked me for cream for his coffee. (In New Zealand we call it milk).
I bought him a little jug of cream, he said 'not what I want' so I bought him back whipped cream. He insisted on cream. After thinking a while I bought him milk and he was like a cat with his cream and left me a huge tip too.