Chris believes that anyone who listens to pop music is an idiot. one day, chris realizes that the song he is dancing and singing along with on the radio is the newest pop music hit. chris now decides that listening to pop music is not so bad after all. chriss attitude change is best explained by

Chris's attitude change is best explained by cognitive dissonance.

It refers to the fact that a person may be experiencing thoughts and feelings which are not really consistent, and which may change, sometimes drastically. In Chris's case, he hated pop music, until he actually listened to one pop song and liked it, and then changed his opinion.