This may not fit into the catagory, but I recently had a guest call and ask about the details regarding our chicken dish (bad sign off the bat, IMO). I described it as being stuffed with a vegetable mousse, in a black truffle sauce. The response? "So it has chocolate in it". I was bewildered, then explained truffles are a type of mushrooms in this instance. I then re-read the description. Again, she replied, "so it has chocolate in it". "Um.. no, what makes you think that, ma'am?". "Well it has MOUSSE in it!". I had to detail to her that mousse is a preparation method, and not exclusive to chocolate. I also commonly hear people mispronounce haricots vert as "harry cot vert". Always makes me giggle.