The 72-year-old designer has hit out at his fellow sartorialist, claiming the 79-year-old Chanel creative director ''doesn't have to'' dress in the way he does, teaming black sunglasses with a signature black suit.
Roberto told The Hunger magazine: ''Just because you are an artist you don't have to dress like that. Karl Lagerfeld, he looks ridiculous.''
Cavalli isn't the only person to have mocked Lagerfeld's sense of style - his mother once told him he looked like an ''old dyke'' in hats.
He said: ''I love hats, in a way, but when I was a child, I'd wear Tyrolean hats, and my mother - I was something like eight - said to me, 'You shouldn't wear hats. You look like an old dyke.'
''Do you say such things to children? She was quite funny, no?''
However, Karl also recalled his father being more supportive of his fashion choices - after he threatened to ''die'' from cold weather if he couldn't have a particular coat.
He said: ''I remember one time in winter in 1956 - it was beyond cold.
''And I went to see my father at the George V with only a suit on. He said to me, 'But you will die! You will get pneumonia!'
''And I said, 'I prefer to die than to wear another coat than the robe style in blue cashmere in the Dorian Gray window. If not that one, I prefer to freeze.' So he bought the coat.''