Imagine sucking the will for someone to live. I thought of a way but I admit it's not really fun but good form of torture.
You chain someone to a wall in a dark, damp, room. Feed and water them only through an enema but only give enough each day so they always feel hungry and thirsty but they live. No light. Nothing to do. Just hanging there doing nothing always hungry and thirsty. (Feel free to "accidentally" skip a day or two on feeding)
Pretty soon they wont wanna live anymore and will be begging for death. If you want, fulfill their wish and put em out of their misery. Or for an alternative leave em there. I'm sure they'll die by sheer force of will.
Or not. Who knows. =P