Used to describe a person, usually a nagging wife, that constantly babbles and complains about even the smallest of issues. This person will usually express their resentment or displeasure in a public place such as a grocery store or restaurant.
Yammering Netty literally means Clamorous Toilet; from the
verb Yammer: To utter or say in a complaining or clamorous tone; and the noun Netty: The British slang word for public or outside toilet. - See also: Chatter Box
Herold took Alice out to a nice restaurant and all she did was babble about how he never takes her anywhere nice. Alice is such a Yammering Netty.