If you believe Sigmund Freud, a baby first experiences pleasure while sucking on its mother's breast. (For simplicity's sake, let's suspend for the moment the argument that not all children are breast-fed.) The mouth, then, becomes the child's first source of gratification. Pacifiers, thumbs and-further down the road-other mouths, cigarettes, lollipops and the like become stand-ins for that first oral fixation.
So why then are so many people terrified by the sight of something that they, as infants, likely touched, saw and tasted?
Freud toyed with the idea that weaning generates separation anxiety-separation from the mother is the child's first experience of loss. The child represses this anxiety.
It can be argued, then, that the unexpected glimpse of a breast dredges up all those awful feelings the kid experienced way back when, but since the feelings were repressed, the individual isn't quite sure why he's made so uncomfortable by the thought of seeing the bare breast.
(This theory is perhaps best applied to John Ashcroft, who spent $8,000 on curtains to cover up the partially nude bronze statue of a woman at the Department of Justice building.)
There's also the theory of the retaliatory breast. When a child is weaned from its mother, its first source of pleasure is taken away. The child develops a love/hate relationship with the breast and a desire to bite it in revenge. There's also a sense, however, that if he or she takes a bite out of the breast, the breast will, in turn, bite back.
These are theories, mind you. For those of us who maintain composure at the sight of an exposed breast, we'll take credit for being just a little less neurotic.