The eight-piece boy band and Lola Saunders went head-to0head in Sunday night's sing-off, with Lola being sent after the judges sent it to deadlock.
But even though the judges had nothing to do with the outcome and it was all down to public vote, Katie, 38, took to Twitter to do what she does best.
She wrote: "Stereo sh*ts are coming back. Like syphilis, once you have it – it never goes away. Will send you mad in the end.
"Stereo Gits are off to Indian call centres Simon hired to thank them for their invaluable help #xfactor [sic]"
The accusatory and offensive tweets were met with anger from Twitter users. "Why do you have to be so rude about everyone? Have they ever done anything to you? No!" one wrote.
Another blasted: "Your so vile, rude & such a b*tch towards everything! Never known such a nast person [sic.]
But some didn't disagree with the social commentator, with one agreeing: "No way #itsafix they can't sing n they defo can't stand in a line [sic]."
In the sing-off Lola sang Natural Woman, while Stereo Kicks chose Pink's Perfect.
Louis Walsh and Cheryl of course opted to save their own acts, while Mel B sent Lola home and Simon, based on the sing-off, decided to save her.
Katie previously heaped praise on Lola, saying: "Lola is de-lovely and delicious. If this is a competition to find one of life's true gems, then it has unearthed a beauty."
Do you think the right person went home?