One of the more awkward "unwritten rules" for converts to learn is shomer negiah. People just tell you not to touch men or women, but with little to no details. Or worse, they only tell women not to offer their hand to the rabbi for a handshake! Few people take the time to explain it.
The natural consequence of this lack of knowledge is in social situations. It's not polite (even by Jewish standards) to just start asking "Alright, who's shomer negiah here? You? To what degree?" Yes, remember that some people and some groups have their own standards (or younger/single people and our "rationalizations"). They don't even have to make sense, but they're the rules people come up with for themselves.
The result of this rare island of Jewish politeness is that you should just assume everyone else is shomer negiah unless you actually know otherwise. Don't make assumptions or go on gossip. Because if someone tells you one thing, you touch that person, and then they tell you they're shomer negiah, you're going to feel like a jerk.
How does this play out in real life? On my Birthright trip, everyone assumed that everyone else was shomer negiah. Coming from a part of the world that doesn't seem to have any concept of shomer negiah, that was weird enough for me! However, near the end of the trip, people began to be comfortable enough to speak about it, and it turned out that many people were not shomer negiah, even though I was convinced otherwise!
The "take away"? If you're around orthodox Jews, don't touch the opposite sex. It'll work itself out from there. And you'll always be "right."