Emberrassing outie [I Have An Outie Belly Button]

So today we went shopping and whilst in the mall I noticed someone looking at me as is they wanted to say something to me. So I asked what was the matter and he said he wasn't comfortable with my belly button. At first I was wondering how he saw it but he then told me that my navel was poking out of my buttoned shirt so he could see it and I wasn't aware of that.

I was quite emberrassing.


What should I do?