Start off by thinking of fifteen people you know:
You're trying to make this a good test, so get as wide a range as possible. Different religions, online and offline, different ages, etc. If you act differently with different people (even if you're quite open about that), pick people who make you act and feel a variety of ways. Write them down on a sheet of A4.
... done that?
Now invite them all to a dinner party next weekend.... or just think about doing so. Scared at all? Those are probably your walls. It's interesting to see both which combinations of people scare you, and also which combinations don't. Sometimes that's an indication of where you can be more open.
Idea stolen from Kate Barnstein.