I have come across more than one immutable travel law over the years:
1) Never be the first person to board a flight from Japan to the US on an American carrier - you simply ensure yourself an extra inspection of your bags and your person that renders you the 50th person to board and no overhead space for your luggage anywhere near your seat. I guess all those people flying on JAL to JFK are a much safer lot that do not require added security
2) Never look inside the kitchen in a restaurant in China (perhaps anywhere but I am sure about China). Like a moth attracted to the flame, I am always tempted to see what goes on beyond the often dirty plastic sheeting that for some reason not clear to me serves as a doorway to many restaurant kitchens in China. Do I really mind that the person preparing my hot peppered chicken is both smoking over and sweating into my food? Perhaps not, because I keep going back to the same place and have never gotten sick there. Do I mind when I see a small rodent scurry across the kitchen floor? Yes, I do and I do not return to those restaurants. Sometimes ignorance is bliss.
3) Always hit the “do not disturb” button in your hotel room before getting in the shower or going to the toilet. Anytime I forget this law travel, results in some well intentioned service person (the exception to this rule is 99% of US hotels) delivering laundry, wanting to check the mini-bar or arriving with a “welcome drink”.
4) If you are not sure what a button means on a Japanese toilet - DO NOT push it. I think every member of my family learned this lesson the hard way. My memorable moment was before teeing off at a Japanese golf course many years ago. I pressed a button and knew it was a bad idea when I heard a hydraulic noise and then remembered that I had been warned to “beware of high tech toilets in Japan”. Before I could manage to get up and out of my stall (I was enjoying the warmth of the toilet seat on a cool fall morning); I was soaked by the spray that was supposed to clean my private area rather than soak my golf attire. I had to endure the walk of shame past several people who saw the “gaijin” come out of the locker room area dripping on his way to the first tee.