unfriend – verb – To remove someone as a ‘friend’ on a social networking site such as Facebook.
As in, “I decided to unfriend my roommate on Facebook after we had a fight.”
Whilst at first glance a lazy construction, simply just gluing the prefix 'un' onto the noun - when to convey the meaning properly one would write "to remove from one's 'friends' list" -, no doubt it shall escape in the wider lexicon with as greater ease as it has assumed itself into the vernacular of the 'Yoot' and all Web2.0 applications, like Facebook, Twitter et al.
Mind you, no doubt someone in Dr Johnson's time wrote precisely the same sentiment when the word 'deflower' first violated the dictionaries of English. Speaking of which, in his time, perhaps this new word would have then been rendered 'unbefriend'.