Trivium‘s Matt Heafy has inserted himself into the ongoing beef between Machine Gun Kelly and Slipknot, criticising the former for his “16-year-old pop punk cosplay identity.”MGK sparked an uproar this month when he hit out at the veteran masked band at Chicago’s Riot Fest, saying onstage: “You wanna know what I’m really happy that I’m not doing? Being 50-years-old wearing a fucking weird mask on a fucking stage, talking shit.”His onstage diss came after Taylor appeared to dismissively allude to