Slaughter the melon. (I personally, don't hold with "seedless" fruit. Neutered fruit! It just does not make any sense.) Puree large chunks in blender with enough water to make it liquid. Strain to remove pulp and seeds. Repeat til you fill up 3/4 of the pitcher. ('Bout 1/2 a good size watermelon.)
Add maybe 1/2 cup sweetener, say organic cane sugar, to about a cup of the strained liquid in the blender. Juice up 2-3 limes and add to mixture. Toss in a little mint, or not. Blend til sugar dissolves. Add back to the pitcher and stir well. Fill pitcher with ice/ more water to taste.
Call up your friends and serve up. And, yeah, add vodka if it's that kinda day. I don't judge.
Guaranteed to make your watermelon live up to it's "muy bueno" potential.