D’oh! :smack:
Tammy Wynette’s D.I.V.O.R.C.E. spells out the title and several other words in its lyrics (and is the only song I can think of in which the title itself is a spelling).
The Magnetic Fields, “Washington D.C.”
“W-A-S-H-I-N-G T-O-N, baby, D-C”
Sufjan Stevens, “They Are Night Zombies!! They Are Neighbors!! They Have Come Back From The Dead!! Ahhhh!”
Several, including I-L-L-I-N-O-I-S and some towns in Illinois.
I was thinking of Crazy Mary (no L-O-I-T-E-R-I-N-G around) but then thought of the Spongebob Squarepants Campfire Song:
C-A-M-P-F-I-R-E S-O-N-G Song
It’s the Ennnnnn-cyclopedia! E-n-c-y-c-l-o-p-e-d-i-a! 12 letters!
And of course
FIREINCAIRO
And Billy Connolly’s parody version of that song also contains a 10 letter word, which is spelled out twice - “Quarantine.”
ETA: If you’re wondering what the bleeped out bit is in that video, it’s “f’ing c.”
“Everything’s O K-A-L-A-M-A-Z-O, O what a gal” is what sprang to my mind.
I think the longest spelled out lyrics are probably found in the Hot Chip/Diplo song “Shake it Over and Over.” The spelling goes on so longer - almost a minute - that I’ve never been able to figure out what they’re spelling after the first two words. Start at 5:15 and listen to see if you can figure it out.
K-I-S-S-I-N-G, S-E-X-I-N-G, C-A-S-I-O, P-O-K-E [?], Y-O-U, M-E, I, repeat.
If made-up words count, then I believe the winner would have to be Supercalifragilisticexpialidocious, which is spelled out in the song.
You are my favorite person in the world right now.
Did you know that they call Kris Kross “the d-a-double d-y-m-a-c”?
“F-I-F-T-Y C-E-N-T and S-N-double O-P”
From Snoop Dogg’s verse on 50 Cent’s ‘P.I.M.P.’ - which seemed longer in my head but is quite short now that I’ve typed it out.
While it is a list of letters, it is not actually spelling anything out. You lose 5 points and a turn.
How could all of you baby boomers forget M-I-C-K-E-Y-M-O-U-S-E?
According to Big Bird, it is.
Not the longest but I always like Janet Jackson’s “Miss You Much”
M-I-S-S you much
It also bugs me that the Hall & Oats song is titled “Method Of Modern Love” but the spelling is Method Of Love. Doesn’t work for me 
One of Neil Innes’ songs for Meet the Rutles -
"Do I have to spell it out? C-H-E-E-S-E-A-N-D-O-N-I-O-N-S oh no! /
Metal machine/
Keep yourself clean/
Be a has-been
Like a dinosaur."
I believe the sentence is:
Ab kid ef-key jeckel min ah-per stoove-witzes