A chatastrophe is any typically sudden, disastrous event that occurs during online chat- whether in chat rooms or private messaging.
Room Two was noted as a peaceable room of cozy fellowship chat amongst civilized habitués. After Room One experienced the chatastrophe of a vengeful bot-loading booter, Room One chatters jumped ship and found their way over to Room Two like so many flotsam-borne rats. This sat uneasily upon the regulars of Two, as the Oners were a virtual rogues gallery of the more virulent personality disorders. In their turn, the Room Two chatters regarded the influx of Oners as a chatastrophe.
When you lose your chat history of previous conversations, and can't remember anything about someone you previously chatted with.
(Nick): Jennifer, right?
(Jennifer): I don't remember you, who are you?
(Nick): oh, sorry, I'm Nick
(Jennifer): Sorry, I've lost my chat history, I don't remember you, I have chatnesia