I remember watching an Eyewitness science video when I was around 4 years old, and it showed a hognose snake and explained that its defense strategy against predators was to roll over on its back and emit a putrid smell like that of a dead body from a place near its genitals, I think within the cloaca. I rewinded that VHS and watched it over and over again to the point of annoying my dad.
Later on, when I first began masturbating, I imagined that the feeling of succumbing to death overtaking one’s body would be incredibly pleasureable/orgasmic. I took this a bit further and liked to fantasize about death occurring through sex, either because the sex was somehow fatal or because in order to die a person had to be fucked by Death (not a stupid grim reaper, but I guess the conceptual entity). I liked imagining how the person would be scared of dying at first but eventually enjoy submitting to their fate.
I also tried to embalm or mummify dead lizards and insects as a kid and it excited me but I didn’t recognize it as sexual excitement, the way somebody mentioned earlier. It also fascinated and excited me to track the progress of decomposition in dead animals, or watch the time-lapse films of decomposition in nature shows.
Also, for some reason the scene in E.T. where they find his motionless body and later when he died excited me, and I liked to imagine masturbating or fucking a person as they died. I remember also being turned on by the myth of Hades and Persephone.