In terms of flop Broadway musicals, BRING BACK BIRDIE is a favorite, with my favorite songs being "When Will Grownups Grow Up" and "Well, I'm Not."
I also like "You Gotta Have Dancing" from the Strouse-Adams A BROADWAY MUSICAL, and find that song running through my head a bit, although I don't love that entire score.
Favorite score to a flop film musical is LOST HORIZON. Terrible film, but some nice songs away from the film, especially the fun duet between the two ladies ("Different people look at life from different points of view; if you really want the things I have, just help yourself, I give them all to you.")