@Anarchy99 it's slang for not being part of the so called, "in group." Obviously it applied to the military first of all but sometime in the 2000's Hollywood A listers started applying it to us normal people.
In the context of my friend - I work in tourism and hospitality and he was a guest who sort of stuck to me and kept in contact when he went back to England - when he was talking about the athletics championships being quite saucy, as it were, I was skeptical of him, although quite physically fit for a normal person having torrid affairs with Olympic standard athletes. The, "in group" in this scenario.
I had always thought of it being quite a closed off and insular community that kept themselves to themselves and didn't mix with people that weren't 24/7 training, eating a very strict diet, going to physio etc. A, "civilian" just wouldn't be on their wavelength, somehow.
Plus, I wrongly thought that their idea of a big night out was having a marinade on their skinless chicken breast, a small bottle of alcohol free beer and going to bed at ten o'clock instead of half past nine.
More bluntly, I just didn't see a nice looking bloke who liked a good pizza and going clubbing having one night stands with the likes of Nico Young or whoever. But allegedly, there's more party time and more Catholic tastes in potential partners in track and field athletics than I knew about.
Which is a good thing, I think.