Flaming Denethor is not an adjective!noun, whatever badslashers may think. It is an exclamation of dismay used by the PPC. The term was coined by Artemis, founder of the Bad Role-play Department. It originated upon the release of Peter Jackson's version of The Return of the King, since many PPCers were... surprised... at his portrayal of the demise of Lord Denethor.
"Flaming Denethor" is also the name of a Bleepka cocktail. The exact recipe may be buried somewhere in the Board archives. In the meantime, it's probably safe to assume that this drink is served on fire.