I think almost all of them are virgins. I'm just not sure about Sanji and Franky. Sanji was popular with women at the Baratie. As one of the few Mugiwara Pirates who are not asexual, living on the Sunny must be torture. That would explain his behavior. Jimbei always seemed asexual to me, and I have even less doubt that Luffy, Zoro and Nami are asexual too. And yes, I think Robin is also drier than the desert of North Africa. Brook... I'm not sure, but I don't think he's had much success with women with his perverted nature. Chopper and Usopp keep their virginity for Milky and Kaya.