I didn't actually think that this particular scene could be understood in any other way....
The Scene in Question
And the Line
Westley: ...There's a shortage of perfect breasts in this world...
From context alone, I find it nearly impossible to understand how one could be confused by this line....
But we can at least have a look at the definition and incorrect concept that 'breast' is used colloquially significantly differently in different english speaking regions.
From Oxford Dictionary:
Either of the two soft, protruding organs on the upper front of a woman's body which secrete milk after childbirth.
A person's chest, especially when regarded as the seat of the emotions.
And a third little tidbit:
The English word breast derives from the Old English word brēost
(breast, bosom) from Proto-Germanic breustam (breast), from the
Proto-Indo-European base bhreus– (to swell, to sprout). The breast
spelling conforms to the Scottish and North English dialectal
pronunciations. The Merriam-Webster Dictionary states that "Middle
English brest, [comes] from Old English brēost; akin to Old High
German brust..., Old Irish brú [belly], [and] Russian bryukho"; the
first known usage of the term was before the 12th century.
The word breast as in, bosom, or mammary glands has a seemingly long history in many languages, with nearly the same pronunciation and spelling for nearly a thousand years...and continues on to this day, in all English speaking regions, and apparently western germanic linguistic family groups...at the minimum.
- The fore part of the body, between the neck and the belly; the chest; as, the >breast of a man or of a horse.
- Either one of the protuberant glands, situated on the front of the chest or >thorax in the female of man and of some other mammalia, in which milk is secreted >for the nourishment of the young; a mamma; a teat.
The meaning of 'breast' as a singular can be slightly confusing assuming the context is missing entirely.
However our film scene is extremely obvious as to what the meaning of breasts can only be. Not only did Westley say breast in the plural "breasts", Buttercup is a woman with breasts about to stab herself, and Westley is quite obviously sexually attracted to her. To consider that he cares about her chest, compared to her breasts is...surprising at most. (This should be a little funny of course)
It is certainly the mammary gland breast that is intended to be understood.