Defriending frenzy 

In social networks, a defriending frenzy is a situation where an oversupply of friends leads to rapid, out-of-control deletion by the account owner. This situation often results in the accidental deletion of real friends, leading to refriending requests.

John: What's this friend request? I thought we were already friends...

Dave: Sorry dude, I went into a defriending frenzy last night and accidentally deleted you

Defriending frenzy by W_L August 30, 2010

collateral defriending

When the ex-boyfriend or ex-girlfriend of a friend defriends you after they break up.

- So and so defriended me on Facebook. What did I do wrong? I know they broke up and we weren't really friends, but still, collateral defriending hurts.

collateral defriending by TOHITF May 6, 2011

Defriending 

The act of stopping being someone's friend. Letting a friend go.

After defriending him I felt so much better about myself.

Defriending by Snotty milk July 24, 2019

Defriendinition

submitting, in some form, your friend's name as a definition on Urban Dictionary

Inundated by defriendinitions, it is understandable that occasionally a few get by the editors.

Defriendinition by Takkislacky January 31, 2010