While searching for a public domain song for my play about Marilyn Monroe I saw that Irving Berlin's "Do It Again" was written in 1914 and so eligible. But I can't use that song ever because some of the lyrics are incredibly creepy and even a date-rapist's fantasy.
I first heard this song when Terry Gross interviewed Gloria Steinem about Steinem's book about Monroe. What an odd context. Gross said she really liked it.