A statement that one is attracted to (or at least not turned off by) flat-chested females. In the United States at least there is a very strong cultural bias, fed by the media towards women with large breasts being seen as more attractive.
Some people however don't find this to be so, and will often say "anything more than a mouthful is a waste" or some similar comment when the inevitable male bonding "look at the tits on that girl..." conversation comes up. This is essentially a way of pointing out that both for babies and significant others, the breast is perfect if it has nipples and is attatched to a wonderful woman.
See Also: more than a handful's a waste.