Facebook Feud
Facebook Feuds begin because one party (correctly or incorrectly) perceives itself to have been attacked, insulted or wronged by another. Intense feelings of resentment trigger the initial retaliation, which causes the other party to feel equally aggrieved and vengeful. And everyone on Facebook gets to enjoy it.
I can tell from my wife's scowl and intense typing she is having a Facebook Feud with her sister!