Flash point is the temperature at which a substance will burn if exposed to a flame. It's not the auto ignition temp, and it's not the temp at which something will burn if exposed to a spark. And it has zero to do with how easy a chemical goes "poof."
Volatility is the concept you're really talking about, which is the ability of a chemical to evaporate or volatilize. The vapor pressure of a chemical at a given temperature and pressure is the measurement of the chemical's volatility. The higher the vapor pressure, the higher the volatility and the faster it will evaporate. There are highly volatile chemicals that don't have a flash point, because they don't burn.
Flash points are easy to find because they're required information on every Safety Data Sheets (SDS or MSDS) for products sold on the open market so fire fighters can do their job of fighting fires. Vapor pressure measurements are much harder to find.
Someone awhile back must have been hunting for a way to predict volatility, decided flash points would do nicely because they're easy to find, and passed the idea onto a Facebook group or other soap forum. And yet another unkillable science myth is born.