Some shitty horror film that came out in spring of 2015 about a dead chick who kills her friends with computer hacking and supernatural ass-fuckery. Whoever thought this was a compelling plot device should be thrown off the back of a speeding pickup truck and into a river in a body bag, weighed down with cinderblocks.
It is when your friend finds a new piece of ass/interest and you soon find yourself becoming nonexistent to them. Its more common between a male and female friendship then a same sex friendships.
Megan: "Hey have you noticed since Brad started talking to Kelly he stopped talking to me."
Steve: "Sorry to say this but no matter how you look at it you are in The UNfriend-zone."
When one deletes a friend from Facebook because he or she knows that the Facebook friend in question would eventually delete them instead. Preemptive unfriending thus robs the deleted Facebook friend of the joy of being able to delete them.
John: Why'd you delete Bec from you friend list?
Adam: I knew she'd eventually delete me so I wanted to take the satisfaction of unfriending for myself.
John: Ah, a preemptive unfriending.