I am convinced that breast envy does exist. However its not limited to men only; I also believe that women are envious of each other's breasts.
Most women I know have made a comment about some other woman's breasts as in
.... I sure would (would not) want to be built like that
.... Did you see the size of her "breasts"
The thing about Breasts vs Penis envy is that the penis for the most part is covered but the "bulge" is becoming important as to size... I don't think that it will be long before there are advertisements for "fake" penile enhancements in pants that replaces the sock down the pants just to enhance the bulge.
OK, OK, but back to the Breast Envy.
YES, men are envious of a woman's breasts. That is one reason we are so enthralled with them. But it is only one reason.