方 便 Fāngbiàn Convenience

A: 你们中国的服务业真是周到。
     Nĭmen zhōngguó de fúwùyè zhēn shì zhōu dào.
     The service industry in China is really thorough.
B: 你从哪看出来的？
     Nĭ cóng nă kàn chū lái de?
     wher did you come up with that?
A: 你们的服务行业常常贴着“为顾客提供方便”，这样就可以很方便找到卫生间。
     Nĭ men de fú wù háng yè cháng cháng tiē zhe "wèi gù kè tí gōng fāng
      biàn," zhè yàng jiù ké yĭ hĕn fāng biàn zhăo dào wèi shēng jiān.
      The service industry here in China has put signs up everywher with the
      sentence: "providing customers with convenience,"which helps us find
      the toilet so easily.

Analysis
In China, the phrase 方便(fāngbiàn) has two meanings. One means "convenient" and the other means "going to the washroom." But, in China's service industry, it only means convenient. So in this joke, 'A' only knows the second meaning, thereby misinterpreting the meaning of the sentence.