1) A social virgin is a person who is new to social activities/events. 2) One who does not socialize enough. 3) A person lacking social skills.
Mark: "Hey, why is Tom acting so weird? Doesn't he get out and do things?"
Sam: "No. This is his first time he's actually gone out to just do stuff other than shopping. He's still a social virgin. Just let him adjust and do new things."