Another rock festival another tough set for Machine Gun Kelly.

The rapper-turned-punk rapper has pissed off heavy metal giant Slipknot's many fans by feuding with the masked band's lead singer Corey Taylor -- MGK says a planned collab with Taylor fell apart because Taylor's verse sucked, whereas Taylor pulled receipts suggesting he was the one who deaded the feature.

At the Aftershock Festival in Sacramento over the weekend angry Slipknot fans threw bottles and tree branches at MGK to show their displeasure.

This ups their game from the Louder Than Life festival in Louisville a few weeks ago, during which Slipknot nation just booed him.

MGK acknowledged his rocky reception in Sacramento from the stage.

"How the f*ck you feelin' Aftershock?" he reportedly asked the crowd. "Mixed opinions. I love you so much. This morning I was like, 'Do we get on the plane and go to this?' I was sitting there thinking about the last festival we did where this 10-year-old got her poster ripped up just for liking me. I'm doing this show for her and everyone who came to see us."