Commonly used as a respond when promoted for an explanation for you griefing or humiliating someone for your own amusement.
Lesser used to describe someone's self humiliation.
Earliest origins have been traced back to the online video game Everquest on the Tallon Zek server.
I spawn camped the noob for an hour until he cried. It was FFMNFY.
Dragging your daddy issues onto the internet is FFMNFY.