Known for creating artworks by vomiting coloured milk onto canvases, Millie Brown stuck two fingers down her throat during "Swine", shocking the Texas festival crowd.
But despite the fierce backlash amid accusations of 'bulimia chic', Brown insists her unusual technique does not affect her health or diet.
Demi Lovato attacked Brown on Twitter for "glamourising eating disorders", writing: "Bottom line, it's not 'cool' or 'artsy' at all."
"Whether we intend to or not, artists influence people of ALL ages and unfortunately what people see, people do," she continued.
"Hair, clothes and sometimes misinterpreting things, therefore using the excuse of art to engage in self-destructive behaviours. I've been through a s**t ton, more than any of you know, and I sympathise for everyone's struggle.
"But people emulate what they see celebrities do or let happen, and that's why I had to say something, to the people who don't understand the art in it, that bulimia isn't cool and it won't get you on stage with your favourite artist."
In response, Brown posted a screenshot of the "Skyscraper" singer's tweet from September last year, in which Lovato said: "I think people are too judgemental on artists today. Artists have and always will have the right to express themselves in any way they want."
Brown added "But yet to bash Gaga?", before tweeting her own post:
Brown first vomited over the Gaga when she threw up a glittering turquoise liquid onto her dress in the music video for "Exorcist Interlude".
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Brown tweeted at the "Applause" singer in February, after the pop star praised her "artist and friend".
Reactions to Brown's 'art' has been mixed with the majority of responses critical.
"There's a big difference between expressing yourself and causing intentional harm to yourself and others," wrote one Twitter user, while another commented: "I'm going to murder someone by using sword dancing and call it art! Art has no limitations right?!"
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