From what Canadian football fans are wearing to a Viagra substitute,
More on watermelon from Wikipedia:

The Oklahoma State Senate passed a bill on 17 April 2007 declaring watermelon as the official state vegetable, with some controversy surrounding whether a watermelon is a vegetable or a fruit.

The citrulline in watermelon (especially in the rind) is a known stimulator of nitric oxide. Nitric oxide is thought to relax and expand blood vessels, much like the erectile dysfunction drug Viagra, and may even increase libido.

Fans of the Saskatchewan Roughriders of the CFL started a tradition of hollowing out a watermelon and wearing it as a makeshift football helmet (the color of the Roughriders is green). During the 2009 Grey Cup in Calgary (between the Montreal Alouettes and the Roughriders), thousands of watermelons had to be imported to Calgary supermarkets to prevent a shortage being caused by Rider fans.

The town of Chinchilla in Queensland, Australia, holds a biannual festival celebrating all things melon.

The ten-lined June beetle is often affectionately referred to as a watermelon beetle, due to the green, striped pattern on its back.

It is the symbol of the Turkish city, Diyarbakır.

The 'Melitopolski' has small, round fruits roughly 28–30 cm (11–12 inches) in diameter. It is an early ripening variety that originated from the Volga River region of Russia, an area known for cultivation of watermelons. The Melitopolski watermelons are seen piled high by vendors in Moscow in summer. This variety takes around 95 days from planting to harvest.[23]

The 'Densuke' watermelon has round fruit up to 25 lb (11 kg). The rind is black with no stripes or spots. It is grown only on the island of Hokkaido, Japan, where up to 10,000 watermelons are produced every year. In June 2008, one of the first harvested watermelons was sold at an auction for 650,000 yen (US$ 6,300), making it the most expensive watermelon ever sold. The average selling price is generally around 25,000 yen ($ 250).

In Japan, farmers of the Zentsuji region found a way to grow cubic watermelons, by growing the fruits in glass boxes and letting them naturally assume the shape of the receptacle. The cubic shape was originally designed to make the melons easier to stack and store, but the cubic watermelons are often more than double the price of normal ones, and much of their appeal to consumers is in their novelty. Pyramid-shaped watermelons have also been developed and any polyhedral shape may potentially also be used.