Since a watermelon looks like it's ripped off the screen of like a Super Mario Bros video game and is wonderful at exploding because of its red flesh and is even more excellent at housing molten aluminium, it very probably is the world's funnest fruit to play with. Here's another fun trick you can do with ol' mellie: 'skin' it.
It's nothing more than a party trick and doesn't require too much special skill. Just get two similar shaped watermelons, shave down one while cutting the other in half and then insert the 'skinned' watermelon into the shell of the other. Magic!