This poster is part of a series entitled "Nicht das, was Sie erwarten" -- meaning "Not what you expect."
In this one you cut open a coconut and find it is a grapefruit inside.
My interpretation of this is that even very well-meaning people in Germany, who fully understand how dreadful the Holocaust was, have gotten somewhat ODed on somber Holocaust exhibits.
These posters are meant to convey the message that the Jewish Museum Berlin is not only a Holocaust museum, but shows a lot more as well -- all the ups and downs of two thousand years of Jewish life in Germany.
Second photo: Another example. In this one you open an oyster and find there is a fried egg inside, sunny side up.

