I know that not all of them have been shown yet, but my favorites are Mihawk, and Donqiouxte Doflamingo.
"Yo; I was a reindeer livin' out in 'da snow! But then this old geeza' doctor brought me into his home! After healin' my wounds, I felt real phat. Then, old docta' Hiruk gave me this blingin' hat! My family beat me, shunt me, but it's all tight. Because I'm doin' my doctor remedies all night. I look like freak with my Human Human fruit. But now I'm with some gangsta' pirates who like to steal loot! All the girls like my blue nose. Yeah; it's the way that I get the Record scratching. Usopp's the guy with all 'da glory. He's my main man with all his tight stories. Zolo's Santoryu skills are on ice. You betta' watch out, or you gonna get sliced! Sanji's the cook servin' up the main dish. Don't mess with him, unless that's your wish. Luffy's 'da captain with the straw hat! His Gum Gum skills are real real tight. Vivi's the princess of Alabasta. Now we gotta head there, and we betta' do it faster!"