It happens a lot in Cologne, Germany.

We have a lot of breweries inns for the local beer, called Kölsch, local dialect for “Colonian”. All of them have a menu item called “Halve Hahn”, again local dialect for "Half a Rooster”. Now, even many Germans expect they would get one half of one of these, wouldn't you?

What you actually DO get is this:

(© Superbass / CC BY-SA 4.0 (via Wikimedia Commons), 2018-10-28-Halve Hahn-9090, CC BY-SA 4.0).

It is a rye bun, butter, medium aged Gouda, onions and (very important!) mustard. I usually do not need the butter, I put the mustard onto the rye bun and top that with onions and the cheese. But then, I am considered a heretic.

So, how come the name? The accepted version goes like this: a young Wilhelm Vierkötter, who came to Cologne from a rather rural place called Wahlscheid, wanted to celebrate his birthday with some friends in one of the aforementioned breweries. As a practical joke on his friends, he arranged with the waiter that he would boastfully order “halve Hähne” (back then in the sense of half a chicken), exciting expectations, only for the waiter to serve what is now known as a Halve Hahn. Allegedly, they all took it well and had a good laugh. Since all of them were regulars, they started to order the rye bun with cheese and condiments by asking for a “Halve Hahn”.

So, hth.

PS Pro tipp for visting a Colonian brewery inn: The waiters will bring you a new beer as soon as about a finger’s width left in you glass. Put a coaster on top of your glass to prevent it. I have seen some _very_ drunk Americans in those inns.