Crushed to Death
You think animals that eat you are bad? Perhaps even worse is an animal that is being ordered to murder you. Such is the case of execution by elephant. Observed in the late 19th century, the punishment was brutal. Note that first the criminal was tied to the leg of the elephant by his waist, and taken for a bloody trot around the city. After that, the criminal was made to kneel and place his head on a stone. The elephant crushed the accused's head with his foot.
While being crushed whole is awful, also consider the unpleasant alternative of dying after only an appendage has been crushed. Toxins build up at a crush site, including large amounts of potassium that can cause cardiac arrest and myoglobin, which can result in kidney failure -- even after the object is removed. Dying from being crushed even after you've had the good fortune of getting out from under the object? A Worst Way to Die, indeed.