Not much to say really on the topic… Except this:
1. To remove someone from your Livejournal, MySpace, Facebook, or other social networking site. Doing this is often seen as a passive-aggressive move, telling the person without telling them that you no longer want to be friends. It’s also commonly a response to drama. Defriending someone often causes more drama. There are sometimes valid reasons for doing this.
That’s the definition of ‘defriending’ from Urban Dictionary. I think it quite hits the nail on the head.
We didn’t have these issues before Facebook. But, finding out someone’s not interested in being friends because they’ve removed themselves on FB is always gonna be a shocker.