boob envy

when small chested girls constantly look at the chests of others

(Noun)
The resentful desire of another woman's bigger or more beautiful breasts. Commonly remarked upon when one female is caught glimpsing into another woman's bosom with a look of envy on her face.

The opposite should really be called reverse boob envy or small boobs envy.

(Noun)
The resentful desire of another woman's smaller breasts. The opposite of the more common and well-known boob envy, in which a woman envies another female's bigger boobs. Reverse boob envy, also known as small boobs envy, is not well known to most men, but is felt by many women to be true, since small breasts are often more practical, and not seldom just as beautiful as bigger jugs.

(Noun)
The envious feeling a woman experiences when she wishes she had smaller, perkier breasts. Commonly remarked upon when one woman is caught glimpsing at another woman's breasts with a look of envy.