Everyone, everywhere is wearing Ami Paris. Why?

Alexandre Mattiussi is excitedly showing me around the offices of his brand Ami Paris, a classical space overlooking the Place des Victoires in the city’s 2nd arrondissement. He points to an enormous bouquet of flowers, sent to him by the actor Issa Rae, who attended his runway show in Paris in June; also a sculpture by Samuel Salcedo depicting three “world leaders” in their underwear with silly hats on. Mattiussi requested the Spanish artist paint his brand’s logo – a capital…