This is easy! LAST KISS by J. Frank Wilson. I get nauseated by it. Somebody did a cover of it for a movie soundtrack a few years ago and it was just as illin'. I'd rather be locked in a room and forced to listen to Tiny Tim for a week than ever hear Last Kiss even one more time.
Ugh, I'd rather listen to every bad song listed in this thread (10 times over) than to watch a second of American Idol. That's definitely my least favortie music related thing.