There's something about water that makes its characters the butt of the joke. We tried several focus groups with them, particularly Aquaman, and these are the results.
First, we showed them the picture of Batman, and they all went "Woooow!"; we showed them Superman, and they all went "Oooohhhh!; with Wonder Woman they just went breathless; but with Aquaman it was just "ROFL". Literally.