I've never had my clothes off around someone in a sexual situation, not even my shirt, but I've had sex, and I'm not a virgin.
Losing your viriginity is up to you and what you believe the act of having sex to be. In my opinion, even giving someone oral is sex, because of the situation you're in.
If they ask if you're a virgin, just say something equally insulting like 'Why, do you want to ->-bleeped-<- me?' 'Ask your sister' etc etc. In the long run, it's none of their business what you've done, or with whom.
I say if you've had sexual relations with someone, then you're no longer a virgin, no matter the gender of the participants.