In Japan they have square watermelons
Watermelons are popular gifts in Japan. They also use them for a game where they have to smash them blindfolded. But it’s an expensive game because square watermelons aren’t cheap (they generally cost in the range of $100 to $160, but maybe that’s not too much for a country with the third largest economy in the world).
The curve-averse watermelons were first developed for ease of transport and fit in the fridge more easily but they have since become a popular novelty product.
Triangular and even heart-shaped melons are not uncommon either. The melons are grown in shaped containers and are very hard to grow (hence the price).