This is not worth an answer

If you think you can carry it off - "Only on laundry day." If you are playing it safe - "Only when I'm interviewing."

Usually not this formal. However I want to assess the degree of formality by doing a binary search on the number of days that I am employed at FB and calibrating eventually to an equilibrium formal level.

My recruiter made it pretty clear that the recommended attire was business casual (jeans + a nice shirt) and that anything more than that would be overdressed. Also, while Facebook pays for the hotel and airfare directly, you can expense your meals, transportation, etc. just like you can with pretty much any other company in the world.