According to the Guiness book of World Records the song with the longest title is "I'm a Cranky Old Yank in a Clanky Old Tank on the Streets of Yokohama with My Honolulu Mama Doin' Those Beat-O, Beat-O Flat-On-My-Seat-O, Hirohito Blues," written by Hoagy Carmichael. Hoagy later claimed that the song ends with "Yank" and the rest was added as a joke.
A favorite long song title of mine is Pink Floyd's "Several Species of Small Furry Animals Gathered Together in a Cave and Grooving With A Pict" from the album Ummagumma.
There is another song by a Swedish Group, Rednex, which is longer than "I'm a Cranky Old Yank etc" - I don't know why it isn't listed as the longest song by the Guiness book of World Records. The title of that song is "The Sad But True Story Of Ray Mingus, The Lumberjack Of Bulk Rock City, And His Never Slacking Stribe In Exploiting The So Far Undiscovered Areas Of The Intention To Bodily Intercourse From The Opposite Species Of His Kind, During Intake Of All The Mental Condition That Could Be Derived From Fermentation." By Rednex.