v. To remove a person from one's list of friends on a social networking site.
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After Jerome Kerviel lost his employer, French investment bank Societe Generale, $7.2 billion, he also lost 7 of his 11 friends on Facebook. Smart move (MVE) by those ex-friends. You never know who's looking at your profile. Of course, at some point, you might be in a similar situation. Because this kind of thing happens all the time. So here's how to defriend that guy who just went into hiding after losing $7.2 billion.
What social-media users are having none of is deception. Members expect authenticity from each other, so they're turned off, say experts, when someone doesn't say they're affiliated with a certain product yet are obvious evangelists. …

Ultimately, abusive practices can backfire as members "de-friend" shills, says Jeff Beringer, vp of the Web relations group at GolinHarris, a telecom-marketing services firm.
—Joan Voight, “The New Brand Ambassadors,” Adweek, December 31, 2007
2005 (earliest)
(v) To remove someone from your livejournal friends list.
"I defriend people who post quiz results. Get a life!"
—Coell, “defriend,” Urban Dictionary, May 14, 2005