This used to happen to me all the time when I lived in Big City. When DH and I were dating, we liked to try various types of authentic world cuisines, and the combination of accents, restaurant noise, and being all mooney-eyed was very, very bad for my listening comprehension.
We tried a shabu-shabu restaurant, and I ordered a tea with milk (I like hot tea with milk, it's what I usually order). The waitress said what I thought was "eh? With milk?" and I said yes, please. When she returned with our drinks, she brought me a tall glass with cold milky tea, a straw, and what appeared to be ice cubes floating in it. OK, we're here to try new things, right?
So I took a sip through the oversized straw, and almost choked to death on what appeared to be a cat's hairball. Turns out it was "bubble tea", and the floating things were balls of tapioca. How we got from "milk please" to "tapioca", I have no idea.
On another evening, we were eating Mexican and I ordered coffee afterwards. The waitress said what I thought was, "Cream?" I know she only said one syllable, and it was a question. I answered "yes please."
She brought me flan. I hate flan. I asked DH afterward, and he said, "yes, you did order it, I was surprised because I know you hate flan." I still can't figure out why someone would order coffee, and you would reply with, "Flan?" DH ate it.
So now, when DH and I are misunderstanding each other, we say, "Flan? You want flan with that?"