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Nebe,
That isn't because gasoline isn't flammable, that's because it has exceeded it's upper explosive limit, meaning it's too rich to ignite.
I don't know who started the myth that liquid gasoline isn't flammable, but they're dead wrong. I think it probably came from people who don't really understand how solvents burn. With solvents, there are two numbers, the flash point which is the temperature the solvent needs to exceed to ignite, and the autoignition temperature when it spontaneously ignites. I just looked it up and for gasoline the flash point is -50 F and the autoignition is 500 F. So as long as it's above minus 50, it will ignite. Another way to say it would be that above minus 50, the vapor pressure of the liquid is high enough to create a flammable fuel air mixture above the liquid, which is probably where the confusion came from.
My guess is that a cigarette either isn't hot enough or the ash slows the transfer of energy to the gasoline. Either way it's not a good idea to throw cigarettes in gasoline.
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