Lady Gaga -- Lets Some Girl VOMIT ON HER During SXSW Show

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.