n. Judging a person based on what songs are on the playlist of his or her digital music player.
But now people are exposing their taste in music — or hopeless lack thereof — at workplaces, college campuses and coffee shops, thanks to iTunes’s ability to share music over a network. Similarly, a quick gander at someone’s iPod reveals the same information.

This has lead to a new kind of music snobbery called playlistism. Music snobs amuse themselves by laughing at a colleague’s collection of showtunes, or the hopelessly pretentious jazz of the goatee-ed guy at the other end of the dorm.
—Leander Kahney, “The Cult of iPod,” Playlist, November 02, 2005
Several recent studies in the US have shown that these lists are not only 'the soundtracks of our lives', but also reasonably reliable personality barometers used to suss out dating partners, job applicants and political candidates.

A study by Palo Alto Research Center in California released last month zooms in on the effects of 'playlistism', a form of musical voyeurism where people can scan one another's musical libraries online.
—Yeow Kai Chai, “You are what you listen to,” Straits Times, May 10, 2005
2003 (earliest)
Forget discriminating people based on their race, religion, gender, or colloquial term for four-square, it’s all about playlistism. That’s right, judging people by their iTunes playlist. Now, I can’t take full credit for this idea; playlistism is really the brainchild of Katie — the iTunes Hatemonger — Brown, but if playlistism ever takes off like the Klu Klux Klan did, I’d be a Grand Wizard.
—Stephen Aubrey, “Adventures in Higher Education: iPod Envy,” The Wesleyan Argus, November 04, 2003