Technically, it IS cannon that Luffy loves soft things. What would be softer than Nami's chest? And another hint, Luffy doesn't take hints or blows to the head very quickly, so he'll keep doing it. Heh, that'd be a hilarious running joke in the manga, Luffy keeps trying to snuggle up to Nami.
luffy: i love boobs (usopp dared me, it can't be helped, she's going to kill me) nami: what seriously? now either i beat you within an inch of your life or you pay me harrassment belli, .... wait both!
lol i love this. you both cosplay them sooooo well. i totally faved this.