Alice Cooper thinks Mumford & Sons are an "offence" to rock 'n' roll.
The veteran 'School's Out' musician thinks the folk band are an embarrassment to rock as they are far too conformist with their clean-cut image and tame behaviour.
He ranted to Fuse.tv: "Mumford & Sons are great at what they do. But it's not rock 'n' roll. Don't call it rock 'n' roll. It's an offence to rock 'n' roll.
"I get they want to be folk rock, and I guess they want to look like everybody else. I'm old school when it comes to if you're in a band, you're an outlaw. You don't play by those rules, you're a rock 'n' roll outlaw."
The 'Eighteen' hitmaker also believes Mumford & Sons aren't passionate enough on stage and lack energy.
Alice added: "It doesn't mean you have to be on drugs, but when you get onstage you don't play the guitar up here [on your chest], and it's not an acoustic guitar.
"You play the guitar down here [by your waist]. It doesn't come from your brain, it comes from your guts. It comes from your groin. It's sexual. It's tribal."
The 65-year-old rocker went on to slam modern musicians in general and claimed they are all too "happy" to make a real impact.
Alice scoffed: "I just feel that this whole generation needs to all eat a steak. Maybe they just need to quit eating vegetarian food and get out there and get some blood pumping in their system.
"Rock 'n' roll is not about 'Happy happy happy, everything's okay. We're The Lumineers, let's clog dance.' Hey, there's a place for that. If I wanted to see a great clog dancing band, I'd see The Lumineers."