"I dont wear a bra except when I want to, and I go topless when I can and want to."
Maybe you (and Melissa, who also responded) could talk about how far "when I can" goes? Are you talking about legal issues, or about offending people, or are there other things that matter to you when deciding?
How about the "want to" part - what makes you want to? Is it mostly being comfortable - you just don't like the feel of clothing that much? Or more about what you can feel that way - wind and sun and movement? Do you ever do it to make a point about equality, or simply to show it's harmless? Do you sometimes like to surprise someone you know to see their reaction? Someone you don't know?
Or would you just rather not say, in case someone says you're wrong?