I always sit in an airplane lavatory, but for a different reason. Just in case I didn't latch the door properly, or in case some hulk of a passenger pushes on the door while I'm in there, I would rather the door hit the knees of a sitting me (where I'm in position to push back) than the seat of a standing me (where I'm in a position to be pushed "in").

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"Yes, but at least mine will be found in a first class seat." -- Peattie and Taylor