The Italian couturier says the popular fashion designer constantly steals his own ideas and gives American style a bad name with his copycat looks.
He ranted to Style.com: ''He's one of the biggest copy designers in the world. I just want to tell him to stop copying me! Stop! All the time I write those comments on Instagram. He copies everybody!
''Americans like Michael Kors! And you love so many other designers who do that - he's not American fashion. He is international fashion made in America. It's not fair. The American women, they all dress the same.''
The outspoken star insists Michael isn't the only designer who is guilty of copying his aesthetic and joked he set up his youth-aimed sister line, Just Cavalli, in 1998 so he could copy himself.
Roberto said: ''Before I [launched] Just Cavalli, I started to see how many people around me were copying me. There was Cavalli style all over, and I said, 'Why am I giving so many opportunities to other people? Maybe I should just start to copy myself.' So I started Just Cavalli to copy myself.''
He also slapped a jet-lagged Taylor Hawkins.
The acclaimed performer had just cancelled touring due to a battle with cancer.