It is like any other "shared experience" type of joke. I am sure in the countries where that candy called a "humbug" is common the majority of the people there had no trouble putting 2 and 2 together to get the joke. We do it all the time, and I enjoy making jokes from movie lines and other shared experiences. But the joke falls flat when we don't have those shared experiences. We are very close to our other english speaking friends on other continents, but there are a few things we just don't understand. And a few things about our culture they just don't get. What is amazing is just how close we actually are and how similar our lives and experiences come together.
Merry Christmas to all.