Can a Guy Tell You're a Virgin?

Hi there Dr. Betty,
I'm in my mid 20's & for various reasons I'm still a virgin. This may sound like a stupid question but would a guy be able to tell I was a virgin when I have sex for the first time? Would it be obvious or am I better off telling him - being a virgin in your mid 20's makes you seem a bit like an anti social freak.
Thanks, D
Dear D,