It's time for the Oxford Dictionary's Word of the Year!
Unfriend - verb - To remove someone as a 'friend' on a social networking site such as Facebook.
Here's a
link to the Oxford University Press blog post announcment, and here's
a related article from MSNBC (with a tiny shoutout to LJ!).
On a personal note, I actually use (and prefer) the term "defriend" instead of "unfriend."