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A few years ago I was told by a Japanese friend "社会の窓" (shakai no mado).
It was explained after some giggling that this is what is said to a man who has inadvertently left his fly open, and that it means literally "society's window".
So why use "society's window" for this situation? Is it actually an additional sense added to a more straightforward older one? Or does it provide some insight into Japanese culture why such wording would be used?
俗語辞書（ぞくごじしょ） (slang dictionary) says that that word was formed because of the radio program called 社会の窓（しゃかいのまど） around 1948-1960, which tried expose anything about society/community.
And people start to called zip fasteners 社会の窓, because it is a hidden place for men.
Also when zip fasteners are opened in any place other than the toilet, they called it 社会の窓（しゃかいのまど）が開いている（あいている）.
