My girlfriend decided all of a sudden that she didn't like a friend of mine that I went to uni with... so she "unfriended" her.
Shouldn't make a difference in the real world, but f**k me! Things are awkward now!
Without facebook it would have simply been a case of doing your best to avoid someone, going through the motions on the odd accasion you bump into them, and just gradually forget about them... but thanks to facebook, it's turned into some kind of statement for everyone to see!
... of course my girlfriend could have just been mature enough to do all the above without making the statement