Mark Liberman has a Language Log post about the implications of the fact that not only do very few of the U.S. Foreign Service officers in Baghdad have any proficiency in Arabic, but what proficiency they have is in the literary (standard) language, known in Arabic as fusha, which is spoken on a daily basis by almost no one in the Arab world. The following anecdote represents the exception that proves the rule:
Parkinson relates the story a friend who was a passionate supporter of fusha and who decided to stick to it exclusively in his family in order to give his children the full advantage of having it as a native language. Getting on a busy Cairo bus with this friend and his three-year-old daughter, the two of them, father and daughter, were separated and the yelling that was necessary to reestablish the contact took place in fusha making the entire bus burst out in laughter.
The quote is from Mohamed Maamouri‘s 1998 paper “Language Education and Human Development: Arabic Diglossia and its Impact on the Quality of Education in the Arab Region” (pdf, html cache), which has much more information if you’re interested in the topic.