What makes you uncomfortable when sitting on an airplane after a long time?

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I can understand that many people are tired of sitting for a long time on the plane, but not so they have the right to encroach on space - inherently cramped - by others. This action is not only impolite but also unsanitary. Although many times remind others, I still feel like salt left the sea. Actually, airlines need to have a code of conduct on the plane, in addition to safety regulations or guidance on escape skills. To me, I don't know what kind of passengers are most uncomfortable with the airplane?