A guy/girl who is well known for taking many people's virginities in an almost predatory fashion, and is often disliked because of this. In many fantasy worlds, goblins are regarded as evil, skulking creatures, taking things that do not belong to them.
Guy 1: Did you hear Dave took another girl's virginity last night?
Guy 2: Yeah, what's that, third one this week?
Guy 1: Yup... what a virginity goblin...