Waterworld/Fridge

Fridge Brilliance

 * The Mariner basically fails pretty hard to emote at all throughout most of the movie (blame Costner). On the other hand...maybe it has something to do with him being part fish. Think about it.
 * Much simpler explanation for the understated acting job: the character spends something like 95-99% of his time with only himself for company, with brief interactions with (likely equally undersocialized or possibly crazy) sailors or suspicious, backwards atoll-dwellers (who he seems well aware would kill him if they knew what he was) being his only interaction when he does communicate with others. He's probably lived that way his entire adult life, why exactly would he be an emotive and charismatic sort?

Fridge Lodgic

 * If there's no one living on Dry Land, how could a map to there exist?
 * They do make a reference to longitude and latitude, but longitude is impossible to determine on a uniform, featureless sphere, so the point is still valid.
 * There were two dead bodies on the island. They could have tattooed the map on their daughter and sent her out to sea to bring others. Of course, there isn't much to go on in the movie for that theory but it makes sense.
 * Here's another headscratcher: Assuming that these Atolls are all built using salvaged materials from the ocean floor, what's keeping it all afloat?
 * The shape? A rock, properly shaped, can float, despite it sinking, well, like a rock in normal circumstances.
 * Indeed, it's called a metal-hulled boat.
 * How did the beach erode away to sand in such a short amount of time geologically?
 * Through whatever process made the air near the peak of Mt. Everest thick with oxygen and of an apparently tropical temperature.
 * Well, to be fair, if the oceans rose that much, the atmosphere would rise with them. And Nepal's latitude is similar to Florida's, so it's not that far-fetched that it would be tropical.