It is probably a good thing that I do not carpool with anyone, because I tend to fixate on one song and play it over and over again.
I can just imagine turning to someone in the passenger seat and saying, "Would you like to listen to the 'Glee' cover of 'Pokerface' five times in a row? Great! Me, too!"
My current can't-get-enough-of-it song is Bruno Mars' first single. It is really sweet, and it is also ridiculously well-crafted.