Don't force it. It just has to be the right moment, ya know?
I completely get the whole joking around thing, though. My class is exactly like that. I guess it just happens when you're close to people. (Most of us have known each other since kindergarten.)
Well, good luck. And in situations like this, you can't take offense if they tease you, because it's just how they're trying to make you feel included, and they don't mean it in a cruel way.