Strapless Bra

One of the "in" things in Japan at the moment are eye-holders that dont have straps like this one - brings me to an interesting question.
When I was in the UK, I noticed many girls who didnt wear a bra in the summer - how did I know? Because my eyes would for some reason automatically lock-on even though I didn't intend to look. I hear that this phenomenon happens to many men.

You would never usually see girls out n about without a bra in Japan and was wondering what the custom/culture is like in your region?