Bikinis are basically underwear made for bathing. Which basically means it is a kind of bra and a pair of panties. Bikinis can be rather sexy, as they cover some of the most sexual parts of the female body and leave that partially for the imagination.
So what is the right size? Some claim it must support the breasts well, some say it must cover well, some say it must fit tight, some say it has to look good.
Some bikinis are simply small. Some too small for big breasts. Again, that is a matter of taste - take a look at how small bikinis can be:
Bianca Beauchamp covers her nipples and basically nothing else. Not very much of her breasts are left for the imagination.
Tylene Buck has a bikini where the top might have a bit more fabric, but in reality it covers just around the same: The nipples and not much more. The bikini bottom also virtually does not cover anything.
Stephanie has a bikini with a bit more fabric. Her breasts are partially covered which gives her a fantastic cleavage.
Crissy Moran chose a leopard bikini even though there is almost too little fabric to reveal the leopard pattern. Like the first two examples it does not leave much for the imagination.
Now for a "bathing suit". A traditional bathing suit has fabric between the top and the bottom, covering the belly and back. Those strings does not really cover anything, revealing - well, all of her body.
Chelsea Charms must have a really hard time finding bikini tops. Well, she probably need them specially tailored. Anyway, this relatively normal sized bikini top covers her nipples and struggle to even cover her areolas. Well, who can blame it :-)
Ines Cudna in the same type of bra, but even though her breasts are pretty large (and pretty!), it fits a lot better. Still enough is left for the imagination.
Penny Mathias also got a too small sized bikini, revealing most of her orbs, except for the nipples. Also she arranged it to reveal the lower part of the breasts, and angle not seen earlier in this post.
Christy Marks is not a skinny girl, and her breasts are not petite either. Anyway she chose a tiny bikini revealing her big soft breasts.
Bikinis this small are rare (at least in my part of the world) in reality, but they can be seen at the beach now and then. Enough reason to go to the beach, though - but there already was that ;)