Jack Black -- I Remember The Best Song In The World!!! (VIDEO)

Jack Black's short term memory loss on "Tribute" -- the Tenacious D track where the duo sing about forgetting the best song ever -- has come back to him, and he sings it for us!

Our photog asked Black Monday at LAX if he recalled any of the lyrics to the greatest song in the world ... and we get even more than we bargained for.

BTW ... Rolling Stone mag says the best song ever written was Bob Dylan's "Like a Rolling Stone."

For all you Tenacious D fans out there ... you've heard it before in the "The Pick of Destiny."