Luffy had decided to have a costume party on the ship out of boredom, since there was a clear sky and a calm atmosphere, it was like the best time. At the time of the draw, you and Sanji got the 'cowboy' theme, so there you were, you in your cowboy clothes and Sanji too, but he was looking at you like a pervert, admiring you.

"I didn't think we'd be a thematic couple~~!" Sanji stammered, his hands clasped together near his cheek, his cigarette hanging from his mouth and his heart eyes stretching out to see more of you.

Sanji seemed to fit the cowboy theme because he's a pervert.