You're sitting in an airplane, and suddenly breaks out into song.
"Flip, Flap and Fly"
Brilliant! Though personally, I thin it would be funnier if it was done over the intercom, and it was either Aces High by Iron Maiden or that scary-ass tunnel song from the original Willy Wonka film.
And another one from life experience, singing "Chanson D'ennui" at school during a free period when your friends have lessons.
And I have found myself humming a few of the songs to myself, or singing them in my head, just because they fit the situation so well.