There was this guy who met a bear in the woods and did the worse thing possible. He ran away. The bear chased him down and vicously mualed him. Then he laid there for I think hours until he was saved. He had nightmares about the mauling for the next few days. And considering all the surgery and morphine the doctors gave him he was asleep a lot. If he had died after all that it would've been pretty terrible.
Ur swimming and dragged under water by a shark. It bit into ur lag and ur blood is all around u. It let's u go and u go back to the surface. U try swing but ur leg has been badly hurt and is holding on by only skin. U then float on ur back and start to get dizzy and then the shark comes back. It bites back into ur other leg and u see it all happen. U see the black eyes and the teeth and the blood. It bring u under and rips of both ur legs. Then a boat come over with ur friends in it. They see u and start bringing u in but the shark cone back and bites u when ur almost on the boat. Ur screaming in pain in the game of tug of war when the shark dives down and u see the horrified faces of ur friend as ur dragged under by the shark. Then the shark let's u go far away from ur friends and u float to the surface all alone. U sit there, legless and alone and die of lack of blood.
Being shot in the stomach at close range. Depending on where you're shot, you've only got an hour to live and since it's at close range, that bullet's burning hot.
being forced to drink drain cleaner. It is highly acidic, and it would be indigestible. imagine the worst heartburn you've ever had. now multiply that by like 10, and imagine it's burning your entire digestive system. the cleaner will slowly burn through your body until it burns a hole in the skin somewhere, and exits your body. But wait there's more! now that your digestive system has been digested, You starve and/or obtain a raging infection. the end .
Drain Cleaner is actually not an acid, it is an alkaline, which is actually worse for your body. The digestive system is proofed against acids, but an alkaline will eat straight through it. Other than that, I commend you for your creativity.