NOFX SICKO

Fat Mike -- put on a solo performance as his alter-ego "Cokie the Clown" at last week's South by Southwest festival in Austin ... covered by the website DyingScene.com.

Mike began the show by passing out the shots to fans and even downed a couple himself. But after a bizarre half hour in which Mike described his friend hanging himself, smothering his dying mother to death and milking a fan, Mike decided to show the crowd a very, very disturbing video.

The video appears to begin just moments before Mike took the stage and shows the singer urinating into a bottle of tequila ... and then serving it to the audience. The video did not appear edited.

Well OK THEN....