The National Anthem was based off an old English drinking song

The song was written for the Anacreontic Society, probably around 1771. The tune was was once thought to have been written by Dr Thomas Arnold, but is now thought to have been written "collectively" by members of the society, led by John Stafford Smith (who now usually gets the credit). The society met every two weeks to get drunk, sing songs and to indulge in some debauchery. Anacreon himself was a Greek poet from about 570BC who was noted for his erotic poetry (in the Anacreontic style that he established) and his drinking songs.

Lyrics below: 

To Anacreon in Heav'n, where he sat in full glee,
A few sons of harmony sent in a petition
That he their Inspirer and patron would be;
When this answer arriv'd from the Jolly Old Grecian "Voice, fiddle and flute, "no longer be mute,
"I'll lend you my name and inspire you to boot,
"And, besides, I'll instruct you, like me, to intwine
"The Myrtle of Venus with Bacchus's Vine."

The news through Olympus immediately flew;
When Old Thunder pretended to give himself airs.
"If these Mortals are suffer'd their scheme to pursue,
"The devil, a Goddess, will stay above (the) stairs.
"Hark, already they cry,
"In transports of joy,
"Away to the sons of Anacreon we''ll fly,
"And there with good fellows we'll learn to intwine
"The Myrtle of Venus with Bacchus's Vine".

"The Yellow-haired God and his nine fusty maids
"From Helicon's banks will incontinent flee,
"Idalia will boast but of tenantless shades,
"And the bi-forked Hill a mere desert will be
"My thunder, no fear on't, on't = on it
"Shall soon do its errand,
"And dam'me! I'll swing the ringleaders, I warrant,
"I'll trim the young dogs, for thus daring to twine
"The Myrtle of Venus with Bacchus's Vine".

Apollo rose up; and said, "Pr'ythee ne'er quarrel,
"Good King of the Gods, with my Vot'ries below:
"Your thunder is useless" - then showing his laurel,
Cry'd "Sic evitabile fulmen, you know!
"then over each head
"My laurels I'll spread;
"So my sons from your crackers no mischief shall dread,
"While, snug in their club-room, they jovially twine
"The Myrtle of Venus with Bacchus's Vine".

Next Momus got up, with his risible phiz,
And swore with Apollo he'd cheerfully join -
"The full tide of Harmony still shall be his,
"But the song and the catch, and the laugh shall be mine.
"Then, Jove, be not jealous
"Of these honest fellows."
Cry'd Jove, "We relent, since the truth you now tell us;
"And swear by Old Styx that they long shall intwine
"The Myrtle of Venus with Bacchus's Vine".

Ye Sons of Anacreon, then join hand in hand;
Preserve unanimity, friendship and love!
'Tis yours to support what's so happily plann'd;
You've the sanction of Gods and the fiat of Jove. While thus we agree Our toast let it be:
"May our club flourish happy, united and free!
"And long may the sons of Anacreon intwine
"The Myrtle of Venus with Bacchus's Vine."

Annotated lyrics here.  via @DefendWallSt.  This inspired me to buy this songbook.