a.k.a. unfriend, defriend
To remove someone as a "friend" specifically on Facebook, for example, "I can't believe it, I just got defaced."
How do you "deface" someone on Facebook? Go to the person's profile, go all the way to the bottom of the left column, you should see a link that says "Remove From Friends." Note: It's considered a serious breach of a friendship to deface someone, and if you decide you want to be friends with this person again, you will have to send a new friend request.
NetLingo Classification: Online Jargon