I'm gonna try to explain this despite being drunk:
Eberyone who's "spontaneously combusted" have been smokers.
Especially smokers in bed
When they fall asleep in bed, with a smoke intheir hand, their clothes catch on fire. If it's left on fire lomg enough, the fat on the human catches on fire.
Fat is especially flammable.
Because a human has alot of fat throughout, especially in the belly/chest area, that the most flammable.
Long story short: Human spontameous combustion comes from smoking in beds that leads to sports couches to make kids smoke in bed cause it's "safer", then they fall asleep in bed, with a lit cigarette,lighting their clothes or bed, leading to the kid burning, leading to their costudents catching fire and eventually thw whole school to catch fire, leading to several death.
