Fandom Twitter slang, A setup account is a profile created by another fandom made to make another fandom look bad. The fake profile will generally tweet out offensive stuff.
“Did you see that (fandom name) account that made 9/11 jokes?”
“Yeah, I think that was a set-up account.”
“Yeah, I think that was a set-up account.”
by Han”IClappedLeia’sCheeks” Solo February 04, 2021
Amongst stans, a "Set up account" is a fake account on the internet that pretends to like an artist they actually hate and says awful things, so the awful things are automatically associated with the artist they dislike