girl

It only depends on how big you are. Too big its no good. Small chested girls can get away with it.

I think its tacky and I'm sure gravity will catch up with her a lot quicker than most.

For me, it's okay if you don't wear a bra when you are at home and nobody's around specially boys. But when the girl will going out it should be nice if she wear a bra so that it's not distracting for the people who will see her nipple sticking under her tees. It will tempt the boys to do something bad on her or not to respect here for not wearing bra, they might think that she's a tart,specially for the conservative countries.