TMZ: Lady Gaga's antics are sometimes vomit inducing, but this is ridiculous ... last night at her SXSW show, she actually let some chick VOMIT ALL OVER HER while she performed.

The vomiter is no amateur ... she's actually a "vomit painter" (actual profession) named Millie Brown, who is known for drinking various liquids and then vomiting them up onto a canvas. In this case ... the canvas was Lady Gaga.

Gaga was playing drums on a song called "Swine" when Brown, after drinking neon green liquid, proceeded to stand over her, stick her fingers down her throat, and vomit the green liquid all over Gaga.

Watch the performance for yourself ... it's sick. Literally.

I call it the "Top The Meat Dress" Syndrome -- like their ancestor Madonna, Gaga and her tribe must keep pushing the envelope visually rather than artistically until they either hit a wall or get traded in for a younger model. Besides, what do you expect her to do -- SING for a living?

And only in America is it possible to vomit for a living without taking part in a medical study...