Bra Fashion!

So, this is going to be a much easier question than the last few, and I expect you all to have an opinion, because in this post I'm going to be talking about fashion!

Yep, I'm under the impression that, unlike most forms of underwear, bras impinge enough on the conscious of society that there are meanings attributed to the various wearing a bra/not wearing a bra choices. But I don't know what the heck those meanings are. I get the impression that bra meanings have changed in the last 50 years, perhaps several times, and I'm not sure what's currently in ascendance.

What is is that you're saying when you don't wear a bra? Is it "I am a skank", or "I am not a skank"? At what point does the plausible deniability engage--is it ok to go braless if people would have to be looking to notice, like if you were wearing a silky shirt that would normally show the bra back when you folded your arms? Is it good, or bad, to wear a bra under one of those tank tops with thin straps that won't hide the bra straps?

Is the purpose of a bra (leaving aside the "holding up boobs" thing) to disguise the fact that you have nipples? I'm confused about how terrible it is to have nipples. I've gotten catalogs that offer fake plastic "always pointy" nipples... On the very same page as nipple-flattening sticky things. On the other hand, I get catalogs that offer underwear with pockets for you to add butt enhancements. I just can't trust the fashion consciousness of the catalogs that come to my zip code.

But I'm sure I can trust you, my wise and perspicacious friends. When is it ok to not wear a bra? Speak, I entreat thee! [hee hee hee hee...]