Oda just stated in the new SBS Volume 83: “Why do Doflamingo and Violet call each other “Doffy” and “Viola”? Actually there is a profound setting about it, but I’m afraid I can’t tell you. Considering ONE PIECE is Shonen manga, I’d like to hide it since the reason is for adult audience. Dressrosa is a nation of passion, indeed!!”
Now this looks so different…