Every HN thread on Bitcoin is 30-50% debate over what "fiat money" means. Every single time.

That's what happens when people hijack words that mean one thing and then use it to mean another; there's a transition period where confusion rules and people argue about definitions. Bitcoin is a fiat currency by the standard meaning of the word, but Bitcoin'ers don't use it that way, it's their fault for creating a new meaning in their community for the word. Fiat doesn't mean government backed, now it does to them, soon someone will add a new definition in a dictionary somewhere and the debate will rage for decades.