An old American folk song, beloved by children, families on road trips, and severely drunk-ass people everywhere.
Ninety-nine bottles of beer on the wall
Ninety-nine bottles of beer
If one of those bottles should happen to fall
Ninety-eight bottles of beer on the wall
A common alternative for line 3 is Take one down, pass it around.

The song continues until there are no more bottles of beer on the wall, or until the audience revolts. It can actually be begun at any number (leading to some true absurdities), and, to the relief of many, there is no real consternation if it ends shy of zero bottles.

Because of the simple progression in the song, it is a mildly popular subject for elementary computer programs (see 99 Bottles of Beer on the Wall in Objective-C et al).