The REAL answer

April 1st, Third Age 3011. Bilbo reads to Frodo and Sam his latest  “translation” of the Silmarillion.
Then Fingolfin mounted on Rochallor his great horse and rode forth alone, and none might restrain him. He passed over Dor-Nu-Fauglith like a wind amid the dust, and all that beheld his onset fled in amaze, thinking that Oromë himself was come. Thus he came alone to Angband’s gates, and he sounded his horn, and smote once more upon the brazen doors, and challenged Morgoth to come forth to single combat. And Morgoth came. But, Fingolfin hid behind the bushes before the door opened forth. And lo! Morgoth found only a bag upon his doorstep, and it burned as the very flames of Udun. And Morgoth, not knowing the foul substance that Fingolfin had filled the bag with before setting it alight, brought his mighty iron-shod foot down upon it with all his indomitable might. And he knew then that he had been deceived, worse even than the time Sauron had affixed to his back the sign proclaiming ‘Kick Me.’
The next year Frodo and Sam would get back at Bilbo by 'toilet papering' Bag End, thus starting a holiday that lasts even to this day.