You don't have to go out and party. I don't and haven't done in the 4 years I've been with Virgin. Did all that with my previous airline and don't want to do it anymore (I'm too old now !)
I've never had a problem getting on with the crew on board and having a laugh but when I get down route I do tend to keep to myself. It's not a problem, I've never had any negative comments and still really enjoy the job. I do go out and about and do things but as I don't drink (don't all die of shock, there are some of us out there) I don't particularly enjoy going out to clubs / bars and watching other people getting drunk. I'll often go out for a nice meal with a couple of other "quieter" people.
Virgin is what you make of it.