From Xander + -ista.
Xanderista (plural Xanderistas)
- (Buffy the Vampire Slayer fandom slang) A fan of the character Xander Harris from the television series Buffy the Vampire Slayer.
1999 April 11, QueenChase [username], “Re: Who does Xander Love?”, in alt.tv.buffy-v-slayer[1] (Usenet):I used to be a major Xanderista. But this season, he's bugged me a lot.
2000 June 7, vicpusateri [username], “Re: OT: Challenge to Regulars”, in alt.tv.buffy-v-slayer[2] (Usenet):Victoria P. is a staunch Xanderista, and will take Xander's part in almost any discussion, even when she knows he is wrong.
2003 February 11, Rose, “Re: So Xander has (Spoilers for "First Date")”, in alt.tv.buffy-v-slayer[3] (Usenet):I recall that Xanderistas did react in the way you describe, even coining the term "Xander Slander".