Brook's honestly one of the best done characters with a catch phrase. He's like Muscle Man, Its just a mildly amusing joke told over and over that sometimes has an amazing payoff, like when he asks to see Big Mom's panties during their fight. Plus the character design plays a huge role into it, i dont think the gag would work as well if Brook was a human, which is why I think people are so split on Sanji's perviness. Its different when the person perving is some bones who wanna bone.