John sprawls out in his middle airplane seat, hogging the armrests on either side as others board the flight in an effort to keep the seat to himself. he is violating which type of norm

The answer to this question is Folkway
Folkway refers to an acceptable way of living that is held by a certain group of people. During the flight, it is considered unpolite to hog the armrests on either side because it will reduce the physical space that held by the people on your left&right. (they probably angry at john but decided not to confront)