You'd never snoop on someones belongings, ever! But.. When Usopp hides a sketchbook from you; you had to look.

So, late at night, when Usopp was dead asleep, you grabbed that sketchbook and ran. You looked at its contents in your hammock, and..

It was full of you. Endless drawings of you, and you never looked prettier! "HEY! That's.. That's mine!" Usopp seemed nervous as he shouted at you.