i think theres a small part of luffy that initially thought uta is adopted/isnt shanks' biological daughter not because he doesn't know what sex is but he believes that shanks gets no pussy whatsoever like yeah shanks is awesome and hes his ideal pirate and his childhood role model but also shanks has no game because luffys framework of shanks is equal parts cool pirate and funny silly loser guy and shanks doesn't make his case any better because in the presence of luffy he goes from being one of the most badass pirates in the world to funny silly loser guy