There's a quote that I feel that goes apt with this kind of thing.
Something like "People are both much better and much worse than you’d suspect, but usually not all at once."
This is to the degree that I might suspect that the person who started this trend was a serious anti-social narcissist who enjoys convincing people to harm themselves in order to seem badass. Though it could just as easily have been someone erroneously trying to prove their "toughness" or whatever and then it just spread on its own.
Still, there's something amusing about seeing some super official people from the fire department having to be like "Don't set yourself on fire. That is bad."
Anyway, I present to you the only legit reason to light yourself on fire: