First off, being called fat isn't fun, endearment term or not. stare
Secondly, it should never matter what size you are to wear a style you love.
Third, telling someone that they sound "fat" for being a D cup is ******** rude, piss off.
Fourth, I think the problem lies more in that there aren't always lolita clothing available for girls of American or European sizes (i.e. taller, CURVIER, bigger foot size, etc). Therein lies the issues I think. The clothing industry is a bit restrictive to who can wear it soley in usually only offering sizes in a very narrow range. Additionally, not everyone can or has the material available to sew.
Now everyone stop fat shaming, be cute and lacy and frilly and love each other.