社しゃ会かいの窓まど

expression, noun

fly (on trousers); flies; zipper

Jocular euphemism for the fly of trousers, literally 'window to society'. Used humorously to point out an open fly.

• おい、社しゃ会かいの窓まどが開あいてるぞ。

  Hey, your fly is open.