'Any girl who utilises breast enlargement procedures to change an A-cup or B-cup into a C-cup or D-cup is clearly deranged and should not be permitted to mate.'
The size of breasts that are bordering on unattractively large. Above average and usually not as good looking or easy to grope as smaller breast sizes.
-"Hey man, look at those boobs, that must be a D cup!"
-"sure, they're nice, all boobs are, but I wouldn't want to get up in there."
-"Good point"