Verb usage evolved from the name of Joss Whedon, creator of the television series Buffy the Vampire Slayer, Angel, and Firefly.
Meanings
(slang, transitive) To invalidate a fan theory or original element of a fanwork through the introduction of new canon or retconning.
Author's note part 2: I'm leaving it to the imagination of the reader what Cordelia saw of her future. Writing that out would be asking to be Jossed. 2000 December 25, Shanna, “Holiday at the Hyperion (2/2)”, in alt.tv.buffy-v-slayer.creative (Usenet):
I have this pet theory which will no doubt be Jossed (Greenwalted?) sooner or later. That Wes's dad is not a Watcher, but someone wealthy and financially connected with the Council (if they have all that influence, at least some of the people involved must know who they are)--in short, some kind of profiteer in the war against the forces of evil. 2001 October 20, Sarah Trombley, “Re: Cut Scenes from Carpe Noctem Script”, in alt.tv.angel (Usenet):
Even if your pet subject was "Jossed" by HBP (in other words, your theorizing was annihalated^([sic]) or impacted by a canon development) we'd love to have your archival works on HPInkPot - just select "pre-HBP" in the "when was this work written?" section. 2005 December 5, heidi8 [username], “New Essay Archive at HPInkPot.com”, in alt.fan.harry-potter (Usenet):