I would have to say the one song that opened my ears to "rock"
Nine Inch Nails - Something I can never have.
I listened to rap up until I was about 16, when one of my friends said that I needed to listen to a CD that he had. I said "I don't want to listen to that crap!" But, I took it home anyways. I chose a random song on the CD, and that was the day that changed my taste in music. I had suddenly realized that this genre that I HATED and refused to listen to was more appealing to me. I stopped listening to rap all together and have not regretted it one bit since...