Well, up till now (even if Oda denies the 'romance' on One Piece) the only woman who has made Luffy react has been Nami, both times in Alabastra (Mr2's clonning and at the bath).

Other than that... Luffy has never reacted to a woman, so my guess is that he is just not interested. Remember how he told off slim-Alvida. I don't think this is a Logia defense, since Boa would be useless against any Logia type Devil User.