Well, you know what "everybody knows..." means. (If you don't, then see The Myths of Wild and Domestic and Everybody Knows...) But can you imagine sharks as playful?
The ReefQuest Centre for Shark Research uses the example of the Porbeagle shark to show that sharks do indeed engage in play.
They cite accounts of sharks playing with floating objects. Plus, the sharks will roll in seaweed, apparently just for the tactile pleasure of it. And they will engage in games of chase when one shark swims off trailing a long piece of seaweed.
On the site they acknowledge that people will try to explain such behavior in ways that perpetuate the 'unthinking killing machine' stereotype, but they say that actual observation makes the "play" explanation the most reasonable and compelling.
And, speaking of actual observation, quote:
Many English sport anglers are well aware of the Porbeagle's curiosity. These sharks are apparently fascinated by anglers' balloon floats (from which bait is suspended), prodding them repeatedly with the snout and sometimes even trying to bite the soft, spheroid wonders; when a balloon that a Porbeagle was exploring 'pops', the shark typically shakes its head then pauses momentarily, as though it simply cannot believe its eyes (fish just don't do that sort of thing!).Unfortunately for the sharks and for our perceptions of the world around us, there's more money to be made from the "killing machine" image.