Everyone has from time to time been visited by the ghost of a particular song, the kind of thing that drifts into your mind but seemingly never drifts away, just lingers behind a potted fern for the appropriate moment. You are sorting socks and realize you're humming Yankee Doodle Dandy, and have been doing so since breakfast. Yikes. Or riding to work, the strains of OOOOOKlahoma...suddenly careen around the corner of your mind, and you know you'll be mentally singing "OOOOOklahoma where the winds blow heavy da da da" for the next eight hours.
It may be "London Bridge," or the Hallelujah Chorus, the entire "Memories", or "Old Man River" (even worse, Stan Freberg's version, "Elderly Man River") anything that plants itself squarely in your brain and sticks, wearing an ever deeper groove in the record up there.
My own bete noir is the Oscar Meyer Weiner song, with alternate endings, and on really bad days, Eddie Fisher singing "Oh My Papa". Feel free to borrow either of these if you feel the need for different material.
Hope this helps.