I was reading Jimmy Cornell's Word Cruising Destinations and there is something that caught my eye which is totally absurd from my point of view: Curtesy Flags. A vessel is required to fly a foreign nation's flag when you enter and operate in its waters. It must be flown from the boat's starboard spreader, it must be the highest up flag, it must be non-raggy, appropriate to the boat's size (about 1 inch per 1 foot of boat length) and must be flown from dawn to dusk or 8am to 9pm (whichever comes first). Not enough, some nations that are part of a larger nation require you to fly their local flag on the 2nd highest position.
Some countries have hefty fines and you may get your Passport confiscated if you don't comply. Even if you comply you may get fined for disrespect if the flag is too small or raggy. Considering the limited space on sailboats it's an absurd requirement and has nothing to do with curtesy. It's straight out nationalism and territorial thinking.