Okay, this isn't from a Broadway musical, but it's from a classic Fred Astaire musical, Royal Wedding... "How Could You Believe Me When I Said I Loved You When You Know I've Been a Liar All My Life?"
Yes, that's the song title. It's the longest song title in any musical from what I read, I don't know in musical film or musical in general.

It's a FUNNY song!
"Wait, wait! I have a question! What is the point in having a door that has a horrible death behind it? Huh? What does that acheive?!"
-The 10th Kingdom