^^ You can suggest tag changes on things. Its the little tag icon next to the "Source" button.
Usually, Big Breasts is applied when the size of the boobs is a focus of the image/work. i.e. its not enough for them to just be big, the bigness has to be the point - character(s) talking about or admiring the size, the owner of the boobs calling attention to them or using them to get attention, etc.