The concept of Spontaneous Self-Combustion first appeared in writing in a Charles Dickens novel. Could the idea be linked with vampirism (burning in light), love (an internal flame of love) or smoking (accidentally inhaling/swallowing lighters, and/or fuel - don't try that at home, or anywhere for that matter)?
The practicality of Spontaneous Self-Combustion is questionable; can a human (mostly made of water) really spontaneously self-combust? Not that I am trying to taint the fun, or anything.
Spontaneous Self-Combustion is a fairly surreal concept to most, so fire-proof underclothing has not yet become necessary. Not yet.