Have a character listen to the TV, radio, music player, or YouTube video and a random song gets stuck in their head. No matter what they do, they cannot stop hearing or singing the song.
What is the song or tune? How do they react when they first hear it? How do they act when they can't get it out of their head?
Plot twist: someone comes along and sings the song just as they get the song out of their heads. What happens next?