Rampardos said:
Also, saying that huge breasts are inherently bad proportions is pretty silly. That's almost like saying chibi is inherently bad proportions. Exaggerated features are not only used in art all the time, it's often the point. Real life anatomy and proportions are used more as a guideline, with some things followed more closely than others. It doesn't mean it can't be deviated from for the sake of cuteness appeal or sex appeal, as long as its done tastefully.
I agree with the first paragraph, there probably needs to be more focus on quality rather than outright "It's too big, axe it". Of the images I've seen get flagged for having grotesque proportions, some of them were well-done enough, while others lacked that quality and/or went into the realm of absurdity and fully deserved to be cropped. That said, there still needs to be an official "too large" or as said before, that determination is left entirely to what each individual thinks is "too large".
As for the proportions, the connection can't be made there. Chibi is a style, a subgroup of the anime/manga style. Just sticking out-of-place huge boobs on a person is not a style. Well, to be precise, there is a style that exaggerates and draws attention to certain objects, but I doubt we're supposed to be tolerant of that. Where does it stop? Are we supposed to approve images with horrendously oversized arms, feet, hands, fingers? No, we'd say they have terrible proportions and axe them. Breasts, hips, whatevers are the same.