When the bowl you're roasting flares up and burns uncontrollably. Usually when smoking dry herb.
He scorched his eyebrows in a raging bongfire.
Bongfire; the act of getting a bunch of people together for a giant bonfire in which you burn nothing but marijuana (and perhaps some kindling).
Jack: "Hey man, are you coming to my bongfire tonight?
Frank: "Nah man, that stuff fries your brain cells."