Answer: Zuzu violated a FOLKWAY.
Explanation: FOLKWAY can be defined as a belief, culture, custom or way of life particular to a group of people, member of society or culture.
Folkway in sociology sets the bar between right and offensive.
The are the unwritten norms for interactions whether casually or in a routine manner.
In the example above, an unwritten rule is to sit at an empty chair far away since there's only one person and so many other empty chairs.