I also wonder in what state some leave their own toilets at home after they have done their business.

I was also puzzled by those diagrams showing how you are supposed to sit on a western toilet seat. But then I watched some bits of one of those crual japanese tv show where their collapsed all the walls of some public toilets when a poor guy was at it (I hope it was an act). To my own surprise the japanese are sitting facing the flusher/wall, not facing the door. Plus you have countries where squat toilets are the norm.

Sex is another area where there are few social norms since you never learn by imitating peers (other than porn which is a terrible model).