OK... I always knew what it meant in the song, but this is not that kinda of blog.
My company uses OPP as an acronym for something related to overseas travel. I have asked and asked what it means, but no one could ever tell me. The people I asked who are around my age would always snicker and reply saying they didn't know (and we would trade that knowing glance that says "we can't make a joke about that because we have to be professional"). The older folks would just flat out say they didn't know - but I would secretly laugh.
Well, when I was in Cuba a couple years ago, one person suggested "Other People's Per Diem" as a possible meaning. Ever since, that is what I have thought it to be (even though I knew it really wasn't).
Today, the mystery was solved. I now know what it officially stands for... but I think I will keep it to myself and continue to let Other People's Per Diem linger in the minds of those who care...