To be fair, if Scott Ian is playing music in a room, he's literally the happiest dude there. Saw him play with both Bungle and Anthrax and he was smiling nearly every moment of both shows. Love that energy, man.
I read an interview where Scott said when they invited him to come and play with them he rocked up to rehearsal thinking it was just to hang out. He said he was shocked when he realised why he was actually there as he’s a big fan. He brings so much energy to whatever he plays. Cool dude.
