This weekend I ordered a burger at a little cafe-type place that featured sauteed mushrooms and swiss cheese as its main supporting flavours, and to my dismay, I found it to be occupied by mayonnaise in addition to the lettuce and tomatos, which I didn't expect but gladly accepted. See, they didn't say it had mayo, which the menu did specifically state about the burger immediately above the one I ordered, so I made an assumption. Thankfully I caught the error and requested a new, mayo-free top bun.
It was delicious too.