DarkTribalNinja

No need to be scared, just jab the creature in the nose to stun him, then quickly straddle the fish so you're positioned between the first dorsal fin and the spiracle.  Position yourself so your facing the same direction as the shark and jam your hand into the gill and grab as much internal tissue as possible and attempt to tear out whatever you're able to get your hands on.  With your other hand, insert your fingers between the upper portion of the eye socket and the eyeball a get a firm grasp on the eyeball itself, the optical nerve will severe with relative ease and you can discard the eye.  If you have a reasonably strong jaw you may also wish to attempt to bite the sharks face, particularly the nose if you're able to reach it.  Fit as much of the shark's face as you can in your mouth, clamp down and use your neck and back muscles to tear away as much flesh as possible, repeat this as many times as you're able to.  Be sure you have a secure hold on the fish, as it will be thrashing wildly in the meantime.  You may also wish to bite off segments of fin located in close proximity of your mouth to inhibit the sharks mobility.  Once the shark loses enough blood it will eventually go unconscious and you'll be able to bite off most of it's face without much of a fight.  I've only tested this on great white and tiger sharks between 15 and 20 feet in length, so I'm not entirely certain it will be effective on larger varieties.  You'll find that a little bit of practice can go a long way and your second shark will go down a lot easier than your first.  You may also wish to practice on more docile marine mammals such as juvenile baleen whales and dolphins, or large oily fish like carp and tuna.